Investment Securities (Maturities of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available for sale securities, fair value
Within 1 year	$ 4,702
After 1 year through 5 years	26,302
After 5 years through 10 years	8,816
After 10 years	10,768
Fair Value	50,588	$ 77,365
Available for sale securities, amortized cost
Within 1 year	4,701
After 1 year through 5 years	26,298
After 5 years through 10 years	8,802
After 10 years	10,771
Amortized Cost	50,572	77,627
Held to maturity securities, fair value
Within 1 year	99
After 1 year through 5 years	12,356
After 5 years through 10 years	36,457
After 10 years	58,470
Fair Value	107,382	74,444
Held to maturity securities, amortized cost
Within 1 year	99
After 1 year through 5 years	12,224
After 5 years through 10 years	36,557
After 10 years	59,091
Amortized Cost	107,971	75,203
U.S. agency mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year	114
After 1 year through 5 years	2,614
After 5 years through 10 years	6,629
After 10 years	9,964
Fair Value	19,321	33,195
Available for sale securities, amortized cost
Amortized Cost	19,301	33,167
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	8,012
After 5 years through 10 years	31,625
After 10 years	49,874
Fair Value	89,511	71,677
Held to maturity securities, amortized cost
Amortized Cost	90,154	72,439
Asset-backed securities [Member]
Available for sale securities, fair value
Within 1 year	4
After 1 year through 5 years	8,939
After 5 years through 10 years	1,743
After 10 years	761
Fair Value	11,447	20,335
Available for sale securities, amortized cost
Amortized Cost	11,418	20,520
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	949
After 5 years through 10 years	4,166
After 10 years	6,851
Fair Value	11,966	941
Held to maturity securities, amortized cost
Amortized Cost	11,950	941
Corporate debt securities [Member]
Available for sale securities, fair value
Within 1 year	2,299
After 1 year through 5 years	5,206
After 5 years through 10 years	0
After 10 years	0
Fair Value	7,505	9,852
Available for sale securities, amortized cost
Amortized Cost	7,482	9,850
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	3,195
After 5 years through 10 years	0
After 10 years	0
Fair Value	3,195	436
Held to maturity securities, amortized cost
Amortized Cost	3,179	436
U.S. Treasury securities [Member]
Available for sale securities, fair value
Within 1 year	872
After 1 year through 5 years	7,114
After 5 years through 10 years	444
After 10 years	0
Fair Value	8,430	8,623
Available for sale securities, amortized cost
Amortized Cost	8,480	8,679
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	220
After 10 years	0
Fair Value	220	219
Held to maturity securities, amortized cost
Amortized Cost	223	223
Certificates of deposit [Member]
Available for sale securities, fair value
Within 1 year	851
After 1 year through 5 years	871
After 5 years through 10 years	0
After 10 years	0
Fair Value	1,722	2,071
Available for sale securities, amortized cost
Amortized Cost	1,720	2,070
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	200
After 5 years through 10 years	0
After 10 years	0
Fair Value	200
Held to maturity securities, amortized cost
Amortized Cost	200
U.S. agency notes [Member]
Available for sale securities, fair value
Within 1 year	349
After 1 year through 5 years	1,558
After 5 years through 10 years	0
After 10 years	0
Fair Value	1,907	1,907
Available for sale securities, amortized cost
Amortized Cost	1,915	1,915
U.S. state and municipal securities [Member]
Available for sale securities, fair value
Fair Value		1,123
Available for sale securities, amortized cost
Amortized Cost		1,167
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	83
After 10 years	1,107
Fair Value	1,190	68
Held to maturity securities, amortized cost
Amortized Cost	1,170	68
Commercial paper [Member]
Available for sale securities, fair value
Within 1 year	213
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	0
Fair Value	213	214
Available for sale securities, amortized cost
Amortized Cost	213	214
Held to maturity securities, fair value
Within 1 year	99
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	0
Fair Value	99	99
Held to maturity securities, amortized cost
Amortized Cost	99	99
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	43
Fair Value	43	45
Available for sale securities, amortized cost
Amortized Cost	43	45
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	363
After 10 years	638
Fair Value	1,001	1,004
Held to maturity securities, amortized cost
Amortized Cost	$ 996	$ 997