Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 14,637	$ 13,454
Other comprehensive income before reclassification, net of income taxes	(253)	654
Amounts reclassified from AOCI, net of income taxes	168	167
Total other comprehensive income (loss), net of tax	(85)	821
Ending balance	14,547	14,322
Other income	6	0
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,229)	(6,295)
Total other comprehensive income (loss), net of tax	(85)	821
Ending balance	(5,314)	(5,474)
Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,190)	(4,895)
Other comprehensive income before reclassification, net of income taxes	(153)	575
Amounts reclassified from AOCI, net of income taxes	2	0
Total other comprehensive income (loss), net of tax	(151)	575
Ending balance	(4,341)	(4,320)
Unrealized gains (losses) on derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(763)	(1,124)
Other comprehensive income before reclassification, net of income taxes	(99)	80
Amounts reclassified from AOCI, net of income taxes	164	165
Total other comprehensive income (loss), net of tax	65	245
Ending balance	(698)	(879)
Net pension and postretirement benefit costs
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(276)	(276)
Other comprehensive income before reclassification, net of income taxes	(1)	(1)
Amounts reclassified from AOCI, net of income taxes	2	2
Total other comprehensive income (loss), net of tax	1	1
Ending balance	$ (275)	$ (275)