Investment Securities - Available-For-Sale Securities (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		$ 79,495	$ 76,602
Unrealized Gains		129	173
Unrealized Losses		(7,198)	(7,069)
Fair Value	[1]	72,426	69,706
Portfolio level basis adjustments, Amortized Cost		88	335
Portfolio level basis adjustments, Unrealized Losses		(88)	(335)
U.S. Treasury and agencies
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		23,722	21,768
Unrealized Gains		11	8
Unrealized Losses		(2,215)	(2,234)
Fair Value		21,518	19,542
Residential mortgage-backed securities | Agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		29,798	28,185
Unrealized Gains		84	104
Unrealized Losses		(2,395)	(2,211)
Fair Value		27,487	26,078
Commercial mortgage-backed securities | Agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		8,696	8,703
Unrealized Gains		0	0
Unrealized Losses		(1,412)	(1,360)
Fair Value		7,284	7,343
Commercial mortgage-backed securities | Non-agency
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		7	7
Unrealized Gains		0	0
Unrealized Losses		(1)	(1)
Fair Value		6	6
Asset-backed securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		6,218	6,713
Unrealized Gains		11	25
Unrealized Losses		(25)	(14)
Fair Value		6,204	6,724
Obligations of state and political subdivisions
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		10,826	10,867
Unrealized Gains		23	36
Unrealized Losses		(1,062)	(914)
Fair Value		9,787	9,989
Other
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		140	24
Unrealized Gains		0	0
Unrealized Losses		0	0
Fair Value		140	24
Excluding portfolio level basis adjustments
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost		79,407	76,267
Unrealized Gains		129	173
Unrealized Losses		(7,110)	(6,734)
Fair Value		$ 72,426	$ 69,706

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.