Investment Securities - Fair Value and Gross Unrealized Losses on Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value
Less than 12 months	$ 6,782	$ 41,346
12 months or more	39,220	8,190
Total	46,002	49,536
Unrealized Losses
Less than 12 months	(841)	(4,295)
12 months or more	(6,827)	(1,751)
Total	(7,668)	(6,046)
U.S. Treasury and federal agencies securities
Fair Value
Less than 12 months	735	2,400
12 months or more	2,077	0
Total	2,812	2,400
Unrealized Losses
Less than 12 months	(7)	(188)
12 months or more	(212)	0
Total	(219)	(188)
Obligations of states and political subdivisions securities
Fair Value
Less than 12 months		0
12 months or more		1
Total		1
Unrealized Losses
Less than 12 months		0
12 months or more		0
Total		0
Agency mortgage-backed securities | Residential mortgage backed securities
Fair Value
Less than 12 months	154	10,078
12 months or more	9,721	938
Total	9,875	11,016
Unrealized Losses
Less than 12 months	(15)	(1,170)
12 months or more	(1,852)	(202)
Total	(1,867)	(1,372)
Agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	5,392	22,083
12 months or more	19,069	3,697
Total	24,461	25,780
Unrealized Losses
Less than 12 months	(787)	(2,487)
12 months or more	(3,807)	(1,026)
Total	(4,594)	(3,513)
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Fair Value
Less than 12 months	134	3,621
12 months or more	4,134	1,059
Total	4,268	4,680
Unrealized Losses
Less than 12 months	(9)	(272)
12 months or more	(588)	(248)
Total	(597)	(520)
Asset-backed securities and other debt securities
Fair Value
Less than 12 months	367	3,164
12 months or more	4,219	2,495
Total	4,586	5,659
Unrealized Losses
Less than 12 months	(23)	(178)
12 months or more	(368)	(275)
Total	$ (391)	$ (453)