Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 14,322	$ 15,308	$ 13,454	$ 17,423
Other comprehensive income before reclassification, net of income taxes	(760)	(1,221)	(104)	(3,519)
Amounts reclassified from AOCI, net of income taxes	190	(16)	355	(61)
Total other comprehensive income (loss), net of tax	(570)	(1,237)	251	(3,580)
Ending balance	13,844	14,427	13,844	14,427
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,474)	(2,929)	(6,295)	(586)
Total other comprehensive income (loss), net of tax	(570)	(1,237)	251	(3,580)
Ending balance	(6,044)	(4,166)	(6,044)	(4,166)
Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,320)	(2,187)	(4,895)	(403)
Other comprehensive income before reclassification, net of income taxes	(416)	(980)	159	(2,764)
Amounts reclassified from AOCI, net of income taxes	0	0		0
Total other comprehensive income (loss), net of tax	(416)	(980)	159	(2,764)
Ending balance	(4,736)	(3,167)	(4,736)	(3,167)
Unrealized gains (losses) on derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(879)	(473)	(1,124)	88
Other comprehensive income before reclassification, net of income taxes	(344)	(242)	(263)	(755)
Amounts reclassified from AOCI, net of income taxes	188	(18)	352	(66)
Total other comprehensive income (loss), net of tax	(156)	(260)	89	(821)
Ending balance	(1,035)	(733)	(1,035)	(733)
Net pension and postretirement benefit costs
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(275)	(269)	(276)	(271)
Other comprehensive income before reclassification, net of income taxes	0	1	0	0
Amounts reclassified from AOCI, net of income taxes	2	2	3	5
Total other comprehensive income (loss), net of tax	2	3	3	5
Ending balance	$ (273)	$ (266)	$ (273)	$ (266)