Long-Term Debt and Shareholders' Equity (Amounts Reclassified from AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension and post-retirement
Interest and fees on loans	$ 488	$ 532
Income tax expense	89	2
Net income	322	14
Net unrealized gains (losses) on derivatives and other | Amounts reclassified from AOCI
Pension and post-retirement
Interest and fees on loans	15	3
Income tax expense	4	1
Net income	$ 11	$ 2