Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 17,981	$ 17,038	$ 15,596
Other comprehensive income before reclassification, net of income taxes	(1,088)	936
Amounts reclassified from accumulated other comprehensive income, net of income taxes	(236)	(224)
Total other comprehensive income (loss), net of tax	(1,324)	712	844
Ending Balance	17,423	17,981	17,038
Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	567	115
Other comprehensive income before reclassification, net of income taxes	(965)	455
Amounts reclassified from accumulated other comprehensive income, net of income taxes	(5)	(3)
Total other comprehensive income (loss), net of tax	(970)	452
Ending Balance	(403)	567	115
Unrealized gains (losses) on derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	476	250
Other comprehensive income before reclassification, net of income taxes	(137)	466
Amounts reclassified from accumulated other comprehensive income, net of income taxes	(251)	(240)
Total other comprehensive income (loss), net of tax	(388)	226
Ending Balance	88	476	250
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	0
Other comprehensive income before reclassification, net of income taxes	0	0
Amounts reclassified from accumulated other comprehensive income, net of income taxes	0	0
Total other comprehensive income (loss), net of tax	0	0
Ending Balance	0	0	0
Net pension and postretirement benefit costs
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(305)	(339)
Other comprehensive income before reclassification, net of income taxes	14	15
Amounts reclassified from accumulated other comprehensive income, net of income taxes	20	19
Total other comprehensive income (loss), net of tax	34	34
Ending Balance	(271)	(305)	(339)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	738	26	(818)
Total other comprehensive income (loss), net of tax	(1,324)	712	844
Ending Balance	$ (586)	$ 738	$ 26