Investment Securities (Summary) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 60,648		$ 57,212
Securities available for sale debt securities, unrealized gains	698		854
Securities available for sale debt securities, unrealized losses	(1,071)		(448)
Securities available for sale, fair value	60,275		57,618
Held to Maturity Securities, Amortized Cost, Total	19,850		18,513
Securities reclassified to equity investments	100		100
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale equity securities, amortized cost			587
Securities available for sale equity securities, unrealized losses			(2)
Securities available for sale equity securities, fair value			585
Accounting Standards Update 2016-01 [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities reclassified to equity investments	600	$ 600
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	60,648		56,625
Securities available for sale debt securities, unrealized gains	698		854
Securities available for sale debt securities, unrealized losses	(1,071)		(446)
Securities available for sale, fair value	60,275		57,033
Held to Maturity Securities, Amortized Cost, Total	19,850		18,513
Held-to-maturity securities, unrealized gains	108		224
Held-to-maturity securities, unrealized losses	(505)		(172)
Held-to-maturity securities, fair value	19,453		18,565
Debt Securities [Member] \| US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	16,307		14,432
Securities available for sale debt securities, unrealized gains	117		173
Securities available for sale debt securities, unrealized losses	(224)		(84)
Securities available for sale, fair value	16,200		14,521
Held to Maturity Securities, Amortized Cost, Total	749		741
Held-to-maturity securities, unrealized gains	25		37
Held-to-maturity securities, unrealized losses	(30)		(13)
Held-to-maturity securities, fair value	744		765
Debt Securities [Member] \| Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	28,211		25,534
Securities available for sale debt securities, unrealized gains	68		121
Securities available for sale debt securities, unrealized losses	(660)		(249)
Securities available for sale, fair value	27,619		25,406
Held to Maturity Securities, Amortized Cost, Total	16,126		14,503
Held-to-maturity securities, unrealized gains	22		77
Held-to-maturity securities, unrealized losses	(446)		(139)
Held-to-maturity securities, fair value	15,702		14,441
Debt Securities [Member] \| Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,174		2,443
Securities available for sale debt securities, unrealized gains	334		336
Securities available for sale debt securities, unrealized losses	(14)		(21)
Securities available for sale, fair value	2,494		2,758
Held to Maturity Securities, Amortized Cost, Total	159		167
Held-to-maturity securities, unrealized gains	2		7
Held-to-maturity securities, fair value	161		174
Debt Securities [Member] \| Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,890		1,960
Securities available for sale debt securities, unrealized gains	1		2
Securities available for sale debt securities, unrealized losses	(83)		(58)
Securities available for sale, fair value	1,808		1,904
Held to Maturity Securities, Amortized Cost, Total	241		407
Held-to-maturity securities, unrealized gains	2		4
Held-to-maturity securities, unrealized losses	(2)
Held-to-maturity securities, fair value	241		411
Debt Securities [Member] \| Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,589		2,603
Securities available for sale debt securities, unrealized gains	7		19
Securities available for sale debt securities, unrealized losses	(29)		(9)
Securities available for sale, fair value	2,567		2,613
Held to Maturity Securities, Amortized Cost, Total	512		538
Held-to-maturity securities, unrealized gains	2		10
Held-to-maturity securities, unrealized losses	(1)
Held-to-maturity securities, fair value	513		548
Debt Securities [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	5,410		5,331
Securities available for sale debt securities, unrealized gains	69		74
Securities available for sale debt securities, unrealized losses	(18)		(8)
Securities available for sale, fair value	5,461		5,397
Held to Maturity Securities, Amortized Cost, Total	191		200
Held-to-maturity securities, unrealized gains	1		1
Held-to-maturity securities, fair value	192		201
Debt Securities [Member] \| Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,067		4,322
Securities available for sale debt securities, unrealized gains	102		129
Securities available for sale debt securities, unrealized losses	(43)		(17)
Securities available for sale, fair value	4,126		4,434
Held to Maturity Securities, Amortized Cost, Total	1,872		1,957
Held-to-maturity securities, unrealized gains	54		88
Held-to-maturity securities, unrealized losses	(26)		(20)
Held-to-maturity securities, fair value	$ 1,900		$ 2,025

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