AFS and HTM Debt Securities, Major Categories (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale debt securities:
Amortized Cost	$ 263,458	$ 272,471
Gross unrealized gains	3,098	1,659
Gross unrealized losses	(573)	(4,218)
Available-for-sale, at fair value	265,983	269,912
Held-to-maturity debt securities:
Held-to-maturity securities, Amortized Cost	145,876	144,788
Gross unrealized gains	2,068	146
Gross unrealized losses	(80)	(2,819)
Held-to-maturity, at fair value	147,864	142,115
Total AFS and HTM Debt securities:
Amortized Cost	409,334	417,259
Gross unrealized gains	5,166	1,805
Gross unrealized losses	(653)	(7,037)
Fair value	413,847	412,027
Held-to-maturity, at fair value	147,864	142,115
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale debt securities:
Amortized Cost	15,334	13,451
Gross unrealized gains	2	3
Gross unrealized losses	(17)	(106)
Available-for-sale, at fair value	15,319	13,348
Held-to-maturity debt securities:
Held-to-maturity securities, Amortized Cost	44,766	44,751
Gross unrealized gains	574	4
Gross unrealized losses	(4)	(415)
Held-to-maturity, at fair value	45,336	44,340
Total AFS and HTM Debt securities:
Held-to-maturity, at fair value	45,336	44,340
Securities of U.S. states and political subdivisions [Member]
Available-for-sale debt securities:
Amortized Cost	44,205	48,994
Gross unrealized gains	968	716
Gross unrealized losses	(78)	(446)
Available-for-sale, at fair value	45,095	49,264
Held-to-maturity debt securities:
Held-to-maturity securities, Amortized Cost	7,948	6,286
Gross unrealized gains	182	30
Gross unrealized losses	(5)	(116)
Held-to-maturity, at fair value	8,125	6,200
Total AFS and HTM Debt securities:
Held-to-maturity, at fair value	8,125	6,200
Securities of U.S. states and political subdivisions [Member] | Nontaxable Preferred Debt Securities [Member]
Available-for-sale debt securities:
Amortized Cost	5,800	6,300
Available-for-sale, at fair value	5,800	6,300
Mortgage-backed securities [Member]
Available-for-sale debt securities:
Amortized Cost	159,930	162,819
Gross unrealized gains	1,685	551
Gross unrealized losses	(314)	(3,167)
Available-for-sale, at fair value	161,301	160,203
Federal agencies [Member]
Available-for-sale debt securities:
Amortized Cost	154,549	155,974
Gross unrealized gains	1,617	369
Gross unrealized losses	(308)	(3,140)
Available-for-sale, at fair value	155,858	153,203
Held-to-maturity debt securities:
Held-to-maturity securities, Amortized Cost	93,105	93,685
Gross unrealized gains	1,312	112
Gross unrealized losses	(71)	(2,288)
Held-to-maturity, at fair value	94,346	91,509
Total AFS and HTM Debt securities:
Held-to-maturity, at fair value	94,346	91,509
Residential [Member]
Available-for-sale debt securities:
Amortized Cost	1,241	2,638
Gross unrealized gains	23	142
Gross unrealized losses	(1)	(5)
Available-for-sale, at fair value	1,263	2,775
Commercial [Member]
Available-for-sale debt securities:
Amortized Cost	4,140	4,207
Gross unrealized gains	45	40
Gross unrealized losses	(5)	(22)
Available-for-sale, at fair value	4,180	4,225
Corporate debt securities [Member]
Available-for-sale debt securities:
Amortized Cost	6,058	6,230
Gross unrealized gains	208	131
Gross unrealized losses	(36)	(90)
Available-for-sale, at fair value	6,230	6,271
Collateralized loan obligations [Member]
Available-for-sale debt securities:
Amortized Cost	32,944	35,581
Gross unrealized gains	165	158
Gross unrealized losses	(114)	(396)
Available-for-sale, at fair value	32,995	35,343
Held-to-maturity debt securities:
Held-to-maturity securities, Amortized Cost	57	66
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Held-to-maturity, at fair value	57	66
Total AFS and HTM Debt securities:
Held-to-maturity, at fair value	57	66
Collateralized debt obligations [Member]
Available-for-sale debt securities:
Amortized Cost	521	662
Available-for-sale, at fair value	649	800
Other [Member]
Available-for-sale debt securities:
Amortized Cost	4,987	5,396
Gross unrealized gains	70	100
Gross unrealized losses	(14)	(13)
Available-for-sale, at fair value	$ 5,043	$ 5,483