Investment Securities (Available For Sale and Held to Maturity Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) $ in Millions	Jun. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Available for sale securities:
Less than 12 months Fair Value	$ 11,875	$ 29,156
Less than 12 months Unrealized Losses	65	212
12 months or longer Fair Value	3,829	12,921
12 months or longer Unrealized Losses	25	226
Total Fair Value	15,704	42,077
Total Unrealized Losses	90	438
Held to maturity securities:
Less than 12 months Fair Value	1,119	52,185
Less than 12 months Unrealized Losses	1	1,095
12 months or longer Fair Value	50,235	0
12 months or longer Unrealized Losses	810	0
Total Fair Value	51,354	52,185
Total Unrealized Losses	811	1,095
Total securities with unrealized losses
Less than 12 months Fair Value	12,994	81,341
Less than 12 months Unrealized Losses	66	1,307
12 months or longer Fair Value	54,064	12,921
12 months or longer Unrealized Losses	835	226
Total Fair Value	67,058	94,262
Total Unrealized Losses	$ 901	$ 1,533
Number of available for sale securities in unrealized loss positions | security	205	627
Number of held to maturity securities in unrealized loss positions | security	625	612
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	$ 1,817	$ 14,816
Less than 12 months Unrealized Losses	6	69
12 months or longer Fair Value	2,976	2,931
12 months or longer Unrealized Losses	21	23
Total Fair Value	4,793	17,747
Total Unrealized Losses	27	92
Held to maturity securities:
Less than 12 months Fair Value	174	51,361
Less than 12 months Unrealized Losses	0	1,086
12 months or longer Fair Value	48,699	0
12 months or longer Unrealized Losses	805	0
Total Fair Value	48,873	51,361
Total Unrealized Losses	805	1,086
Asset-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	866	1,670
Less than 12 months Unrealized Losses	0	13
12 months or longer Fair Value	550	9,237
12 months or longer Unrealized Losses	4	201
Total Fair Value	1,416	10,907
Total Unrealized Losses	4	214
Held to maturity securities:
Less than 12 months Fair Value	945
Less than 12 months Unrealized Losses	1
12 months or longer Fair Value	779
12 months or longer Unrealized Losses	1
Total Fair Value	1,724
Total Unrealized Losses	2
Corporate debt securities [Member]
Available for sale securities:
Less than 12 months Fair Value	867	2,407
Less than 12 months Unrealized Losses	1	17
12 months or longer Fair Value	303	653
12 months or longer Unrealized Losses	0	1
Total Fair Value	1,170	3,060
Total Unrealized Losses	1	18
U.S. Treasury securities [Member]
Available for sale securities:
Less than 12 months Fair Value	6,418	6,926
Less than 12 months Unrealized Losses	51	59
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	6,418	6,926
Total Unrealized Losses	51	59
Held to maturity securities:
Less than 12 months Fair Value	0	219
Less than 12 months Unrealized Losses	0	4
12 months or longer Fair Value	222	0
12 months or longer Unrealized Losses	1	0
Total Fair Value	222	219
Total Unrealized Losses	1	4
U.S. agency notes [Member]
Available for sale securities:
Less than 12 months Fair Value	1,907	1,907
Less than 12 months Unrealized Losses	7	8
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	1,907	1,907
Total Unrealized Losses	7	8
Certificates of deposit [Member]
Available for sale securities:
Less than 12 months Fair Value		474
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		100
12 months or longer Unrealized Losses		1
Total Fair Value		574
Total Unrealized Losses		1
Non-agency commercial mortgage-backed securities [Member]
Held to maturity securities:
Less than 12 months Fair Value	0	591
Less than 12 months Unrealized Losses	0	4
12 months or longer Fair Value	535	0
12 months or longer Unrealized Losses	3	0
Total Fair Value	535	591
Total Unrealized Losses	$ 3	4
U.S. state and municipal securities [Member]
Available for sale securities:
Less than 12 months Fair Value		956
Less than 12 months Unrealized Losses		46
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Total Fair Value		956
Total Unrealized Losses		46
Held to maturity securities:
Less than 12 months Fair Value		14
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Total Fair Value		14
Total Unrealized Losses		$ 1