Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 27,841	$ 25,326	$ 25,326
Other comprehensive income (loss) before reclassifications	(272)	252
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	33	56
Other comprehensive income	(239)	308
Ending balance	27,742	26,692	27,841
AFS transferred to HTM	(253)		(267)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,043)	(2,100)	(2,100)
Other comprehensive income	(239)	308
Ending balance	(1,282)	(1,792)	(1,043)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(33)	(132)	(132)
Other comprehensive income (loss) before reclassifications	(24)	1
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	20	29
Other comprehensive income	(4)	30
Ending balance	(37)	(102)	(33)
Net Unrealized Gains (Losses) on Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(151)	(480)	(480)
Other comprehensive income (loss) before reclassifications	(144)	84
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	13	27
Other comprehensive income	(131)	111
Ending balance	(282)	(369)	(151)
Net Unrealized Gains (Losses) on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(92)	(129)	(129)
Other comprehensive income (loss) before reclassifications	3	3
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	3	3
Ending balance	(89)	(126)	(92)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(793)	(2,168)	(2,168)
Other comprehensive income (loss) before reclassifications	(237)	450
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	(237)	450
Ending balance	(1,030)	(1,718)	(793)
Net Unrealized Gains (Losses) on Hedges of Net Investments in Non-U.S. Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	26	809	809
Other comprehensive income (loss) before reclassifications	130	(286)
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	130	(286)
Ending balance	$ 156	$ 523	$ 26