Investment Securities (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities Available for Sale and Held to Maturity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Available for sale securities:
Amortized Cost	$ 215,873		$ 61,155
Gross Unrealized Gains	6,356		407
Gross Unrealized Losses	997		140
Fair Value	221,232		61,422
Held to maturity securities:
Amortized Cost	0	$ 134,700	134,706
Gross Unrealized Gains		$ 1,400	1,758
Gross Unrealized Losses			365
Fair Value			136,099
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	173,812		45,964
Gross Unrealized Gains	6,007		312
Gross Unrealized Losses	224		121
Fair Value	179,595		46,155
Held to maturity securities:
Amortized Cost			109,325
Gross Unrealized Gains			1,521
Gross Unrealized Losses			280
Fair Value			110,566
Asset-backed securities [Member]
Available for sale securities:
Amortized Cost	23,077		4,970
Gross Unrealized Gains	49		30
Gross Unrealized Losses	645		13
Fair Value	22,481		4,987
Held to maturity securities:
Amortized Cost			17,806
Gross Unrealized Gains			50
Gross Unrealized Losses			85
Fair Value			17,771
Corporate debt securities [Member]
Available for sale securities:
Amortized Cost	11,192		5,427
Gross Unrealized Gains	136		57
Gross Unrealized Losses	106		0
Fair Value	11,222		5,484
Held to maturity securities:
Amortized Cost			4,661
Gross Unrealized Gains			57
Gross Unrealized Losses			0
Fair Value			4,718
U.S. Treasury securities [Member]
Available for sale securities:
Amortized Cost	3,616		3,387
Gross Unrealized Gains	48		3
Gross Unrealized Losses	0		6
Fair Value	3,664		3,384
Held to maturity securities:
Amortized Cost			223
Gross Unrealized Gains			5
Gross Unrealized Losses			0
Fair Value			228
U.S. state and municipal securities [Member]
Available for sale securities:
Amortized Cost	1,493
Gross Unrealized Gains	96
Gross Unrealized Losses	11
Fair Value	1,578
Held to maturity securities:
Amortized Cost			1,301
Gross Unrealized Gains			103
Gross Unrealized Losses			0
Fair Value			1,404
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	1,215		13
Gross Unrealized Gains	16		0
Gross Unrealized Losses	5		0
Fair Value	1,226		13
Held to maturity securities:
Amortized Cost			1,119
Gross Unrealized Gains			22
Gross Unrealized Losses			0
Fair Value			1,141
Certificates of deposit [Member]
Available for sale securities:
Amortized Cost	1,000		1,000
Gross Unrealized Gains	3		4
Gross Unrealized Losses	5		0
Fair Value	998		1,004
Held to maturity securities:
Amortized Cost			200
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			200
Commercial paper [Member]
Available for sale securities:
Amortized Cost	397		394
Gross Unrealized Gains	0		1
Gross Unrealized Losses	1		0
Fair Value	396		395
Available-for-sale securities, current	4,100		2,500
Foreign government agency securities [Member]
Available for sale securities:
Amortized Cost	50
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Fair Value	51
Held to maturity securities:
Amortized Cost			50
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			50
Other [Member]
Available for sale securities:
Amortized Cost	21
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 21
Held to maturity securities:
Amortized Cost			21
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			$ 21
Corporate debt securities issued by financial services industry [Member]
Held to maturity securities:
AFS and HTM securities percentage	32.00%		32.00%
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Held to maturity securities:
Asset-backed securities percentage	42.00%		43.00%
Collateralized Credit Card Securities [Member]
Held to maturity securities:
Asset-backed securities percentage	43.00%		42.00%

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Concentration Risk, Available For Sale And Held To Maturity Securities

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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).

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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 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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