Investment Securities (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities Available for Sale and Held to Maturity Securities) (Details) - USD ($)	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Available for sale securities:
Amortized Cost	$ 273,747,000,000		$ 61,155,000,000
Gross Unrealized Gains	7,932,000,000		407,000,000
Gross Unrealized Losses	463,000,000		140,000,000
Fair Value	281,216,000,000		61,422,000,000
Held to maturity securities:
Amortized Cost	0	$ 134,700,000,000	134,706,000,000
Gross Unrealized Gains		$ 1,400,000,000	1,758,000,000
Gross Unrealized Losses			365,000,000
Fair Value			136,099,000,000
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	230,102,000,000		45,964,000,000
Gross Unrealized Gains	7,162,000,000		312,000,000
Gross Unrealized Losses	177,000,000		121,000,000
Fair Value	237,087,000,000		46,155,000,000
Held to maturity securities:
Amortized Cost			109,325,000,000
Gross Unrealized Gains			1,521,000,000
Gross Unrealized Losses			280,000,000
Fair Value			110,566,000,000
Asset-backed securities [Member]
Available for sale securities:
Amortized Cost	22,234,000,000		4,970,000,000
Gross Unrealized Gains	167,000,000		30,000,000
Gross Unrealized Losses	282,000,000		13,000,000
Fair Value	22,119,000,000		4,987,000,000
Held to maturity securities:
Amortized Cost			17,806,000,000
Gross Unrealized Gains			50,000,000
Gross Unrealized Losses			85,000,000
Fair Value			17,771,000,000
Corporate debt securities [Member]
Available for sale securities:
Amortized Cost	12,653,000,000		5,427,000,000
Gross Unrealized Gains	390,000,000		57,000,000
Gross Unrealized Losses	4,000,000		0
Fair Value	13,039,000,000		5,484,000,000
Held to maturity securities:
Amortized Cost			4,661,000,000
Gross Unrealized Gains			57,000,000
Gross Unrealized Losses			0
Fair Value			4,718,000,000
U.S. Treasury securities [Member]
Available for sale securities:
Amortized Cost	4,733,000,000		3,387,000,000
Gross Unrealized Gains	38,000,000		3,000,000
Gross Unrealized Losses	0		6,000,000
Fair Value	4,771,000,000		3,384,000,000
Held to maturity securities:
Amortized Cost			223,000,000
Gross Unrealized Gains			5,000,000
Gross Unrealized Losses			0
Fair Value			228,000,000
U.S. state and municipal securities [Member]
Available for sale securities:
Amortized Cost	1,489,000,000
Gross Unrealized Gains	131,000,000
Gross Unrealized Losses	0
Fair Value	1,620,000,000
Held to maturity securities:
Amortized Cost			1,301,000,000
Gross Unrealized Gains			103,000,000
Gross Unrealized Losses			0
Fair Value			1,404,000,000
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	1,214,000,000		13,000,000
Gross Unrealized Gains	40,000,000		0
Gross Unrealized Losses	0		0
Fair Value	1,254,000,000		13,000,000
Held to maturity securities:
Amortized Cost			1,119,000,000
Gross Unrealized Gains			22,000,000
Gross Unrealized Losses			0
Fair Value			1,141,000,000
Certificates of deposit [Member]
Available for sale securities:
Amortized Cost	800,000,000		1,000,000,000
Gross Unrealized Gains	3,000,000		4,000,000
Gross Unrealized Losses	0		0
Fair Value	803,000,000		1,004,000,000
Held to maturity securities:
Amortized Cost			200,000,000
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			200,000,000
Commercial paper [Member]
Available for sale securities:
Amortized Cost	200,000,000		394,000,000
Gross Unrealized Gains	0		1,000,000
Gross Unrealized Losses	0		0
Fair Value	200,000,000		395,000,000
Available-for-sale securities, current	0		2,500,000,000
Foreign government agency securities [Member]
Available for sale securities:
Amortized Cost	300,000,000
Gross Unrealized Gains	1,000,000
Gross Unrealized Losses	0
Fair Value	301,000,000
Held to maturity securities:
Amortized Cost			50,000,000
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			50,000,000
Other [Member]
Available for sale securities:
Amortized Cost	22,000,000
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 22,000,000
Held to maturity securities:
Amortized Cost			21,000,000
Gross Unrealized Gains			0
Gross Unrealized Losses			0
Fair Value			$ 21,000,000
Corporate debt securities issued by financial services industry [Member]
Held to maturity securities:
AFS and HTM securities percentage	49.00%		32.00%
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Held to maturity securities:
Asset-backed securities percentage	41.00%		43.00%
Collateralized Credit Card Securities [Member]
Held to maturity securities:
Asset-backed securities percentage	45.00%		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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Amount 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 of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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