Investment Securities (Summary) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 61,907		$ 57,212
Securities available for sale debt securities, unrealized gains	631		854
Securities available for sale debt securities, unrealized losses	(1,327)		(448)
Securities available for sale, fair value	61,211		57,618
Held to Maturity Securities, Amortized Cost, Total	19,593		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
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	61,907		56,625
Securities available for sale debt securities, unrealized gains	631		854
Securities available for sale debt securities, unrealized losses	(1,327)		(446)
Securities available for sale, fair value	61,211		57,033
Held to Maturity Securities, Amortized Cost, Total	19,593		18,513
Held-to-maturity securities, unrealized gains	70		224
Held-to-maturity securities, unrealized losses	(642)		(172)
Held-to-maturity securities, fair value	19,021		18,565
Debt Securities [Member] \| US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	17,054		14,432
Securities available for sale debt securities, unrealized gains	91		173
Securities available for sale debt securities, unrealized losses	(294)		(84)
Securities available for sale, fair value	16,851		14,521
Held to Maturity Securities, Amortized Cost, Total	754		741
Held-to-maturity securities, unrealized gains	19		37
Held-to-maturity securities, unrealized losses	(38)		(13)
Held-to-maturity securities, fair value	735		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	28,694		25,534
Securities available for sale debt securities, unrealized gains	46		121
Securities available for sale debt securities, unrealized losses	(838)		(249)
Securities available for sale, fair value	27,902		25,406
Held to Maturity Securities, Amortized Cost, Total	15,962		14,503
Held-to-maturity securities, unrealized gains	6		77
Held-to-maturity securities, unrealized losses	(573)		(139)
Held-to-maturity securities, fair value	15,395		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	2,034		2,443
Securities available for sale debt securities, unrealized gains	331		336
Securities available for sale debt securities, unrealized losses	(13)		(21)
Securities available for sale, fair value	2,352		2,758
Held to Maturity Securities, Amortized Cost, Total	155		167
Held-to-maturity securities, unrealized gains			7
Held-to-maturity securities, fair value	155		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	2,050		1,960
Securities available for sale debt securities, unrealized gains			2
Securities available for sale debt securities, unrealized losses	(85)		(58)
Securities available for sale, fair value	1,965		1,904
Held to Maturity Securities, Amortized Cost, Total	164		407
Held-to-maturity securities, unrealized gains	1		4
Held-to-maturity securities, unrealized losses	(2)
Held-to-maturity securities, fair value	163		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	2,561		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	2,539		2,613
Held to Maturity Securities, Amortized Cost, Total	502		538
Held-to-maturity securities, unrealized gains			10
Held-to-maturity securities, unrealized losses	(1)
Held-to-maturity securities, fair value	501		548
Debt Securities [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	5,545		5,331
Securities available for sale debt securities, unrealized gains	64		74
Securities available for sale debt securities, unrealized losses	(17)		(8)
Securities available for sale, fair value	5,592		5,397
Held to Maturity Securities, Amortized Cost, Total	187		200
Held-to-maturity securities, unrealized gains			1
Held-to-maturity securities, fair value	187		201
Debt Securities [Member] \| Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	3,969		4,322
Securities available for sale debt securities, unrealized gains	92		129
Securities available for sale debt securities, unrealized losses	(51)		(17)
Securities available for sale, fair value	4,010		4,434
Held to Maturity Securities, Amortized Cost, Total	1,869		1,957
Held-to-maturity securities, unrealized gains	44		88
Held-to-maturity securities, unrealized losses	(28)		(20)
Held-to-maturity securities, fair value	$ 1,885		$ 2,025

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