Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 13,844	$ 14,427	$ 13,454	$ 17,423
Other comprehensive income before reclassification, net of income taxes	(783)	(2,144)	(885)	(5,662)
Amounts reclassified from AOCI, net of income taxes	188	53	541	(9)
Total other comprehensive income (loss), net of tax	(595)	(2,091)	(344)	(5,671)
Ending balance	13,356	13,290	13,356	13,290
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(6,044)	(4,166)	(6,295)	(586)
Total other comprehensive income (loss), net of tax	(595)	(2,091)	(344)	(5,671)
Ending balance	(6,639)	(6,257)	(6,639)	(6,257)
Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,736)	(3,167)	(4,895)	(403)
Other comprehensive income before reclassification, net of income taxes	(668)	(1,616)	(509)	(4,380)
Amounts reclassified from AOCI, net of income taxes	0	0	0	0
Total other comprehensive income (loss), net of tax	(668)	(1,616)	(509)	(4,380)
Ending balance	(5,404)	(4,783)	(5,404)	(4,783)
Unrealized gains (losses) on derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,035)	(733)	(1,124)	88
Other comprehensive income before reclassification, net of income taxes	(115)	(527)	(376)	(1,281)
Amounts reclassified from AOCI, net of income taxes	187	50	537	(17)
Total other comprehensive income (loss), net of tax	72	(477)	161	(1,298)
Ending balance	(963)	(1,210)	(963)	(1,210)
Net pension and postretirement benefit costs
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(273)	(266)	(276)	(271)
Other comprehensive income before reclassification, net of income taxes	0	(1)	0	(1)
Amounts reclassified from AOCI, net of income taxes	1	3	4	8
Total other comprehensive income (loss), net of tax	1	2	4	7
Ending balance	$ (272)	$ (264)	$ (272)	$ (264)