Investment Securities (Summary) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	$ 67,619	$ 63,514
Securities available for sale debt securities, unrealized gains	1,544	710
Securities available for sale debt securities, unrealized losses	(106)	(835)
Debt Securities, Available-for-sale	69,057	63,389
Held to Maturity Securities, Amortized Cost, Total	18,826	19,312
Held-to-maturity securities, unrealized gains	434	118
Held-to-maturity securities, unrealized losses	(50)	(411)
Held-to-maturity securities, fair value	19,210	19,019
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	17,597	18,104
Securities available for sale debt securities, unrealized gains	420	133
Securities available for sale debt securities, unrealized losses	(12)	(137)
Debt Securities, Available-for-sale	18,005	18,100
Held to Maturity Securities, Amortized Cost, Total	772	758
Held-to-maturity securities, unrealized gains	75	28
Held-to-maturity securities, unrealized losses		(23)
Held-to-maturity securities, fair value	847	763
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	5,256	4,933
Securities available for sale debt securities, unrealized gains	89	59
Securities available for sale debt securities, unrealized losses	(6)	(20)
Debt Securities, Available-for-sale	5,339	4,972
Held to Maturity Securities, Amortized Cost, Total	54	182
Held-to-maturity securities, unrealized gains	1	1
Held-to-maturity securities, fair value	55	183
Other [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	2,892	3,821
Securities available for sale debt securities, unrealized gains	126	96
Securities available for sale debt securities, unrealized losses	(1)	(38)
Debt Securities, Available-for-sale	3,017	3,879
Held to Maturity Securities, Amortized Cost, Total	1,795	1,849
Held-to-maturity securities, unrealized gains	85	53
Held-to-maturity securities, unrealized losses	(16)	(28)
Held-to-maturity securities, fair value	1,864	1,874
Mortgage-backed Securities Agency [Member] \| Residential Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	34,130	29,413
Securities available for sale debt securities, unrealized gains	506	104
Securities available for sale debt securities, unrealized losses	(56)	(524)
Debt Securities, Available-for-sale	34,580	28,993
Held to Maturity Securities, Amortized Cost, Total	15,527	15,740
Held-to-maturity securities, unrealized gains	257	32
Held-to-maturity securities, unrealized losses	(34)	(358)
Held-to-maturity securities, fair value	15,750	15,414
Mortgage-backed Securities Agency [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	2,909	2,630
Securities available for sale debt securities, unrealized gains	54	13
Securities available for sale debt securities, unrealized losses	(24)	(66)
Debt Securities, Available-for-sale	2,939	2,577
Held to Maturity Securities, Amortized Cost, Total	89	143
Held-to-maturity securities, unrealized gains	3	1
Held-to-maturity securities, unrealized losses		(1)
Held-to-maturity securities, fair value	92	143
Mortgage-backed Securities Non-agency [Member] \| Residential Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	1,626	1,924
Securities available for sale debt securities, unrealized gains	308	300
Securities available for sale debt securities, unrealized losses	(3)	(13)
Debt Securities, Available-for-sale	1,931	2,211
Held to Maturity Securities, Amortized Cost, Total	140	152
Held-to-maturity securities, unrealized gains	7	2
Held-to-maturity securities, fair value	147	154
Mortgage-backed Securities Non-agency [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	3,209	2,689
Securities available for sale debt securities, unrealized gains	41	5
Securities available for sale debt securities, unrealized losses	(4)	(37)
Debt Securities, Available-for-sale	3,246	2,657
Held to Maturity Securities, Amortized Cost, Total	449	488
Held-to-maturity securities, unrealized gains	6	1
Held-to-maturity securities, unrealized losses		(1)
Held-to-maturity securities, fair value	$ 455	$ 488

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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