| Company | Ranking | Outlook | Date |
|---|---|---|---|
| S&P | A+ | Steady | Could 19 2023 |
| DBRS | A | Steady | Feb 24 2023 |
| DBRS | A (excessive) | Unfavourable | Aug 26 2022 |
| Fitch | A | Unfavourable | Aug 19 2022 |
| Moody’s | A2 | Unfavourable | Aug 05 2022 |
| S&P | A+ | Unfavourable | Could 20 2022 |
| Fitch | A | Steady | Oct 29 2021 |
| S&P | A+ | Steady | Jan 22 2021 |
| Fitch | A | Unfavourable | Nov 06 2020 |
| S&P | A+ | Unfavourable | Jul 24 2020 |
| Fitch | A | Steady | Could 08 2020 |
| Moody’s | A2 | Steady | Sep 27 2019 |
| Moody’s | A2 | Optimistic | Apr 07 2017 |
| DBRS | A (excessive) | Steady | Apr 22 2016 |
| S&P | A+ | Steady | Jul 31 2015 |
| S&P | A | Optimistic | Aug 01 2014 |
| Moody’s | A2 | Steady | Oct 04 2013 |
| Moody’s | A2 | Unfavourable | Feb 13 2012 |
| S&P | A | Steady | Jan 13 2012 |
| S&P | A+ | Unfavourable Watch | Dec 05 2011 |
| S&P | A+ | Optimistic | Aug 24 2011 |
| Moody’s | A1 | Steady | Mar 27 2009 |
| S&P | A+ | Steady | Nov 27 2008 |
| Moody’s | A1 | Optimistic | Jul 31 2008 |
| Fitch | A+ | Steady | Jul 08 2008 |
| Fitch | A | Unfavourable Watch | Could 07 2008 |
| S&P | A | Optimistic | Mar 03 2008 |
| Fitch | A | Optimistic | Jul 23 2007 |
| Moody’s | A1 | Steady | Oct 17 2006 |
| Moody’s | A2 | Optimistic Watch | Mar 09 2006 |
| S&P | A | Steady | Dec 19 2005 |
| Fitch | A | Steady | Oct 11 2005 |
| Moody’s | A2 | Optimistic | Jan 12 2005 |
| S&P | A- | Optimistic | Dec 13 2004 |
| Moody’s | A3 | Optimistic Watch | Oct 06 2004 |
| Fitch | A- | Steady | Sep 21 2004 |
| Moody’s | A3 | Optimistic | Jun 18 2004 |
| S&P | BBB+ | Optimistic | Mar 02 2004 |
| Fitch | BBB+ | Optimistic | Jan 22 2004 |
| Fitch | BBB | Optimistic | Nov 04 2003 |
| Fitch | BBB | Steady | Mar 03 2003 |
| S&P | BBB | Optimistic | Dec 19 2002 |
| Moody’s | A3 | Steady | Nov 12 2002 |
| Fitch | BBB- | Optimistic | Nov 01 2002 |
| Moody’s | Baa3 | Steady | Nov 13 2001 |
| S&P | BBB- | Optimistic | Oct 30 2001 |
| Fitch | BB+ | Optimistic | Feb 20 2001 |
| Moody’s | Ba1 | Optimistic | Nov 30 2000 |
| S&P | BB+ | Optimistic | Nov 09 2000 |
| Fitch | BB+ | Steady | Sep 21 2000 |
| S&P | BB+ | Steady | Nov 12 1999 |
| Moody’s | Ba1 | Steady | Oct 27 1999 |
| Fitch | BB+ | N/A | Dec 22 1998 |
| Fitch | BBB- | Unfavourable Watch | Oct 05 1998 |
| Moody’s | Ba1 | Unfavourable Watch | Oct 01 1998 |
| S&P | BB+ | Unfavourable | Sep 17 1998 |
| S&P | BBB- | Unfavourable | Apr 06 1998 |
| Moody’s | Ba1 | Steady | Mar 30 1998 |
| Moody’s | Baa3 | Unfavourable Watch | Jan 20 1998 |
| Fitch | BBB- | N/A | Aug 08 1996 |
| S&P | BBB- | Steady | Apr 11 1996 |
| Moody’s | Baa3 | Steady | Could 15 1995 |
| S&P | BB+ | Steady | Apr 05 1995 |
| S&P | BB- | Steady | Feb 15 1994 |
