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Derivative Instruments and Hedging Activities - Gains (Losses) on Accounting Hedges and Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Cash flow hedges - Interest rate contracts
Cash flow hedges expected to be reclassified from AOCI			$ (51.0)
Maximum length of time over which forecasted cash flows are hedged			34 months
Borrowings
Amortized cost	$ 759.0		$ 759.0		$ 589.0
Hedged asset, unallocated basis adjustment	1,273.0		1,273.0		703.0
Amortized cost, unalloccated basis adjustment	(1.1)		(1.1)		2.0
Interest rate
Cash flow hedges - Interest rate contracts
Recognized in OCI	(410.0)	$ (4.0)	(748.0)	$ 13.0
Less: Realized gains (losses) (pre-tax) reclassified from AOCI to interest income	(11.0)	(25.0)	(15.0)	(31.0)
Net change in cash flow hedges included within AOCI	(399.0)	21.0	(733.0)	44.0
Investment securities—AFS
Fair Value Hedges - Hedged Items
Amortized cost basis/ carrying amount currently or previously hedged	46,402.0		46,402.0		55,451.0
Basis adjustments included in amortized cost/ carrying amount	(269.0)		(269.0)		217.0
Deposits
Fair Value Hedges - Hedged Items
Amortized cost basis/ carrying amount currently or previously hedged	53,354.0		53,354.0		53,224.0
Basis adjustments included in amortized cost/ carrying amount	(322.0)		(322.0)		149.0
Borrowings
Borrowings
Carrying amount currently or previously hedged	225,898.0		225,898.0		199,274.0
Basis adjustments included in carrying amount—Outstanding hedges	(8,282.0)		(8,282.0)		(6,252.0)
Basis adjustments included in carrying amount—Terminated hedges	(588.0)		(588.0)		$ (625.0)
Equity
Cash flow hedges - Interest rate contracts
Recognized in OCI	131.0	0.0	73.0	0.0
Less: Realized gains (losses) (pre-tax) reclassified from AOCI to interest income	5.0	0.0	4.0	0.0
Net change in cash flow hedges included within AOCI	126.0	0.0	69.0	0.0
Fair Value Hedges \| Income Statement Location [Axis]: us-gaap:InterestAndDividendIncomeOperating \| Interest rate
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in interest expense	322.0	(309.0)	613.0	(802.0)
Fair Value Hedges \| Income Statement Location [Axis]: us-gaap:InterestAndDividendIncomeOperating \| Investment securities—AFS
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in interest expense	(313.0)	320.0	(596.0)	823.0
Fair Value Hedges \| Income Statement Location [Axis]: us-gaap:InterestExpenseOperating \| Interest rate
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in interest expense	(1,297.0)	1,544.0	(2,550.0)	3,862.0
Fair Value Hedges \| Income Statement Location [Axis]: us-gaap:InterestExpenseOperating \| Deposits
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in interest expense	246.0	(29.0)	498.0	(78.0)
Fair Value Hedges \| Income Statement Location [Axis]: us-gaap:InterestExpenseOperating \| Borrowings
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in interest expense	1,055.0	(1,518.0)	2,064.0	(3,790.0)
Net Investment Hedges \| Foreign exchange
Net investment hedges—Foreign exchange contracts
Recognized in OCI	172.0	(968.0)	389.0	(1,404.0)
Forward points excluded from hedge effectiveness testing—Recognized in Interest income	$ (4.0)	$ 30.0	$ 59.0	$ 47.0