Investment Securities - Held-to-Maturity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	$ 82,948	$ 84,045
Unrealized Gains	0	12
Unrealized Losses	(11,799)	(9,969)
Fair Value	71,149	74,088
U.S. Treasury and agencies
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	1,345	1,345
Unrealized Gains	0	0
Unrealized Losses	(42)	(35)
Fair Value	1,303	1,310
Residential mortgage-backed securities | Agency
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	79,805	80,997
Unrealized Gains	0	6
Unrealized Losses	(11,736)	(9,929)
Fair Value	68,069	71,074
Commercial mortgage-backed securities | Agency
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	1,697	1,695
Unrealized Gains	0	6
Unrealized Losses	(21)	(5)
Fair Value	1,676	1,696
Other
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	101	8
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 101	$ 8