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	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Available for sale securities:
Less than 12 months Fair Value	$ 17,289	$ 29,156
Less than 12 months Unrealized Losses	85	212
12 months or longer Fair Value	3,301	12,921
12 months or longer Unrealized Losses	19	226
Total Fair Value	20,590	42,077
Total Unrealized Losses	104	438
Held to maturity securities:
Less than 12 months Fair Value	53,811	52,185
Less than 12 months Unrealized Losses	1,048	1,095
12 months or longer Fair Value	3,673	0
12 months or longer Unrealized Losses	2	0
Total Fair Value	57,484	52,185
Total Unrealized Losses	1,050	1,095
Total securities with unrealized losses
Less than 12 months Fair Value	71,100	81,341
Less than 12 months Unrealized Losses	1,133	1,307
12 months or longer Fair Value	6,974	12,921
12 months or longer Unrealized Losses	21	226
Total Fair Value	78,074	94,262
Total Unrealized Losses	$ 1,154	$ 1,533
Number of available for sale securities in unrealized loss positions | security	266	627
Number of held to maturity securities in unrealized loss positions | security	698	612
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	$ 6,663	$ 14,816
Less than 12 months Unrealized Losses	20	69
12 months or longer Fair Value	1,939	2,931
12 months or longer Unrealized Losses	10	23
Total Fair Value	8,602	17,747
Total Unrealized Losses	30	92
Held to maturity securities:
Less than 12 months Fair Value	52,259	51,361
Less than 12 months Unrealized Losses	1,040	1,086
12 months or longer Fair Value	149	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	52,408	51,361
Total Unrealized Losses	1,040	1,086
Asset-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	975	1,670
Less than 12 months Unrealized Losses	1	13
12 months or longer Fair Value	959	9,237
12 months or longer Unrealized Losses	9	201
Total Fair Value	1,934	10,907
Total Unrealized Losses	10	214
Held to maturity securities:
Less than 12 months Fair Value	723
Less than 12 months Unrealized Losses	0
12 months or longer Fair Value	3,524
12 months or longer Unrealized Losses	2
Total Fair Value	4,247
Total Unrealized Losses	2
Corporate debt securities [Member]
Available for sale securities:
Less than 12 months Fair Value	1,157	2,407
Less than 12 months Unrealized Losses	1	17
12 months or longer Fair Value	403	653
12 months or longer Unrealized Losses	0	1
Total Fair Value	1,560	3,060
Total Unrealized Losses	1	18
U.S. Treasury securities [Member]
Available for sale securities:
Less than 12 months Fair Value	6,587	6,926
Less than 12 months Unrealized Losses	55	59
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	6,587	6,926
Total Unrealized Losses	55	59
Held to maturity securities:
Less than 12 months Fair Value	220	219
Less than 12 months Unrealized Losses	3	4
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	220	219
Total Unrealized Losses	3	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	8	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	8	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	609	591
Less than 12 months Unrealized Losses	5	4
12 months or longer Fair Value	0	0
12 months or longer Unrealized Losses	0	0
Total Fair Value	609	591
Total Unrealized Losses	$ 5	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