AFS and HTM Debt Securities, Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	$ (4,084)	$ (569)
Less than 12 months, Fair value, available-for-sale	116,287	71,006
12 months or more, Gross unrealized losses, available-for-sale	(1,417)	(285)
12 months or more, Fair value, available-for-sale	18,944	12,405
Total, Gross unrealized losses, available-for-sale	(5,501)	(854)
Total fair value, available for sale	135,231	83,411
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(1,559)	(192)
Less than 12 months, Fair value, available-for-sale	41,680	24,418
12 months or more, Gross unrealized losses, available-for-sale	(45)	0
12 months or more, Fair value, available-for-sale	1,257	0
Total, Gross unrealized losses, available-for-sale	(1,604)	(192)
Total fair value, available for sale	42,937	24,418
Securities of U.S. states and political subdivisions [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(186)	(36)
Less than 12 months, Fair value, available-for-sale	3,036	2,308
12 months or more, Gross unrealized losses, available-for-sale	(83)	(15)
12 months or more, Fair value, available-for-sale	610	532
Total, Gross unrealized losses, available-for-sale	(269)	(51)
Total fair value, available for sale	3,646	2,840
Federal agency mortgage-backed securities [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(2,276)	(334)
Less than 12 months, Fair value, available-for-sale	63,258	40,695
12 months or more, Gross unrealized losses, available-for-sale	(1,258)	(248)
12 months or more, Fair value, available-for-sale	15,441	9,464
Total, Gross unrealized losses, available-for-sale	(3,534)	(582)
Total fair value, available for sale	78,699	50,159
Non-agency mortgage-backed securities [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(29)	(4)
Less than 12 months, Fair value, available-for-sale	3,027	1,966
12 months or more, Gross unrealized losses, available-for-sale	(16)	(11)
12 months or more, Fair value, available-for-sale	534	543
Total, Gross unrealized losses, available-for-sale	(45)	(15)
Total fair value, available for sale	3,561	2,509
Collateralized loan obligations [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(28)	(3)
Less than 12 months, Fair value, available-for-sale	4,523	1,619
12 months or more, Gross unrealized losses, available-for-sale	(6)	(4)
12 months or more, Fair value, available-for-sale	581	1,242
Total, Gross unrealized losses, available-for-sale	(34)	(7)
Total fair value, available for sale	5,104	2,861
Other debt securities [Member]
Available-for-sale debt securities:
Less than 12 months, Gross unrealized losses, available-for-sale	(6)	0
Less than 12 months, Fair value, available-for-sale	763	0
12 months or more, Gross unrealized losses, available-for-sale	(9)	(7)
12 months or more, Fair value, available-for-sale	521	624
Total, Gross unrealized losses, available-for-sale	(15)	(7)
Total fair value, available for sale	$ 1,284	$ 624