Investment Securities (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Available for sale securities:
Amortized Cost	$ 356,439	$ 330,248
Gross Unrealized Gains	5,431	7,799
Gross Unrealized Losses	2,248	647
Fair Value	359,622	337,400
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	312,045	283,911
Gross Unrealized Gains	4,862	7,005
Gross Unrealized Losses	2,139	563
Fair Value	314,768	290,353
Asset-backed securities [Member]
Available for sale securities:
Amortized Cost	17,436	18,808
Gross Unrealized Gains	136	174
Gross Unrealized Losses	44	84
Fair Value	17,528	18,898
Corporate debt securities [Member]
Available for sale securities:
Amortized Cost	12,882	12,408
Gross Unrealized Gains	268	388
Gross Unrealized Losses	57	0
Fair Value	13,093	12,796
U.S. Treasury securities [Member]
Available for sale securities:
Amortized Cost	8,814	10,631
Gross Unrealized Gains	21	25
Gross Unrealized Losses	6	0
Fair Value	8,829	10,656
U.S. state and municipal securities [Member]
Available for sale securities:
Amortized Cost	1,623	1,544
Gross Unrealized Gains	100	153
Gross Unrealized Losses	1	0
Fair Value	1,722	1,697
Foreign government agency securities [Member]
Available for sale securities:
Amortized Cost	1,408	1,411
Gross Unrealized Gains	1	2
Gross Unrealized Losses	1	0
Fair Value	1,408	1,413
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	1,209	1,213
Gross Unrealized Gains	39	52
Gross Unrealized Losses	0	0
Fair Value	1,248	1,265
Certificates of deposit [Member]
Available for sale securities:
Amortized Cost	1,000	300
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,000	300
Other [Member]
Available for sale securities:
Amortized Cost	22	22
Gross Unrealized Gains	4	0
Gross Unrealized Losses	0	0
Fair Value	$ 26	$ 22
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Available for sale securities:
Asset-backed securities percentage	58.00%	51.00%
Collateralized Credit Card Securities [Member]
Available for sale securities:
Asset-backed securities percentage	32.00%	36.00%
Corporate debt securities issued by financial services industry [Member]
Available for sale securities:
AFS securities percentage	39.00%	46.00%

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Concentration Risk, Available For Sale

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- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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