Investment Securities (Summary) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	$ 86,344	$ 67,790
Securities available for sale debt securities, unrealized gains	3,553	1,471
Securities available for sale debt securities, unrealized losses	(150)	(98)
Investment securities – available for sale	89,747	69,163
Held to maturity securities, amortized cost	1,438	17,661
Held-to-maturity securities, unrealized gains	184	423
Held-to-maturity securities, unrealized losses	(8)	(40)
Held-to-maturity securities, fair value	1,614	18,044
Debt securities, available-for-sale, accrued interest	242
Debt securities, held-to-maturity, accrued interest	2
Debt securities, available-for-sale, allowance for credit loss	68
Debt securities, held-to-maturity, allowance for credit loss	$ 3
Credit Concentration Risk [Member] | Fitch, AAA or AA Rating [Member]
Debt Securities, Held-to-maturity [Abstract]
Concentration risk, percentage	85.00%
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	$ 17,273	16,150
Securities available for sale debt securities, unrealized gains	954	382
Securities available for sale debt securities, unrealized losses	(2)	(16)
Investment securities – available for sale	18,225	16,516
Held to maturity securities, amortized cost	790	776
Held-to-maturity securities, unrealized gains	142	56
Held-to-maturity securities, fair value	932	832
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	51,202	35,847
Securities available for sale debt securities, unrealized gains	1,737	517
Securities available for sale debt securities, unrealized losses	(11)	(43)
Investment securities – available for sale	52,928	36,321
Held to maturity securities, amortized cost		14,419
Held-to-maturity securities, unrealized gains		270
Held-to-maturity securities, unrealized losses		(26)
Held-to-maturity securities, fair value		14,663
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	1,376	1,515
Securities available for sale debt securities, unrealized gains	243	302
Securities available for sale debt securities, unrealized losses	(16)	(3)
Investment securities – available for sale	1,603	1,814
Held to maturity securities, amortized cost		133
Held-to-maturity securities, unrealized gains		7
Held-to-maturity securities, fair value		140
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	2,824	3,094
Securities available for sale debt securities, unrealized gains	144	42
Securities available for sale debt securities, unrealized losses	(2)	(18)
Investment securities – available for sale	2,966	3,118
Held to maturity securities, amortized cost		59
Held-to-maturity securities, unrealized gains		1
Held-to-maturity securities, fair value		60
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	3,851	3,352
Securities available for sale debt securities, unrealized gains	73	29
Securities available for sale debt securities, unrealized losses	(95)	(9)
Investment securities – available for sale	3,829	3,372
Held to maturity securities, amortized cost		430
Held-to-maturity securities, unrealized gains		4
Held-to-maturity securities, fair value		434
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	5,158	5,044
Securities available for sale debt securities, unrealized gains	105	78
Securities available for sale debt securities, unrealized losses	(23)	(8)
Investment securities – available for sale	5,240	5,114
Held to maturity securities, amortized cost		52
Held-to-maturity securities, fair value		52
Other [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	4,660	2,788
Securities available for sale debt securities, unrealized gains	297	121
Securities available for sale debt securities, unrealized losses	(1)	(1)
Investment securities – available for sale	4,956	2,908
Held to maturity securities, amortized cost	648	1,792
Held-to-maturity securities, unrealized gains	42	85
Held-to-maturity securities, unrealized losses	(8)	(14)
Held-to-maturity securities, fair value	$ 682	$ 1,863