Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 25,326	$ 23,799	$ 23,799
Other comprehensive income (loss) before reclassifications	252	(97)
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	56	82
Other comprehensive income	308	(15)
Ending balance	26,692	24,433	25,326
AFS transferred to HTM	(347)		(374)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,100)	(2,354)	(2,354)
Other comprehensive income	308	(15)
Ending balance	(1,792)	(2,369)	(2,100)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(132)	(131)	(131)
Other comprehensive income (loss) before reclassifications	1	34
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	29	(147)
Other comprehensive income	30	(113)
Ending balance	(102)	(244)	(132)
Net Unrealized Gains (Losses) on Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(480)	(947)	(947)
Other comprehensive income (loss) before reclassifications	84	(30)
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	27	228
Other comprehensive income	111	198
Ending balance	(369)	(749)	(480)
Net Unrealized Losses on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(129)	(145)	(145)
Other comprehensive income (loss) before reclassifications	3	6
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	1
Other comprehensive income	3	7
Ending balance	(126)	(138)	(129)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,168)	(1,400)	(1,400)
Other comprehensive income (loss) before reclassifications	450	(292)
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	450	(292)
Ending balance	(1,718)	(1,692)	(2,168)
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	809	269	269
Other comprehensive income (loss) before reclassifications	(286)	185
Increase (decrease) due to amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	(286)	185
Ending balance	$ 523	$ 454	$ 809