Investment Securities (Investment Securities by Contractual Maturity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost
AFS debt securities: Amortized cost, total	$ 58,145	$ 56,059
AFS equity securities: Amortized cost	0	15
AFS Securities: Amortized cost, total	58,145	56,074
HTM securities: Amortized cost, total	23,892	23,599
Investment securities: Amortized cost, total	82,037	79,673
Fair Value
AFS debt securities: Fair value, total	56,749	55,198
AFS equity securities: Fair value	0	5
AFS securities: Fair value, total	56,749	55,203
HTM securities: Fair value, total	22,919	23,081
Investment securities: Fair value, total	$ 79,668	78,284
Average Yield
AFS debt securities: Annualized average yield, total	1.60%
AFS securities: Annualized average yield, total	1.60%
HTM securities: Annualized average yield, total	2.20%
Investment securities: Annualized average yield, total	1.80%
U.S. Government and Agency Securities
Amortized Cost
AFS debt securities: Amortized cost, total	$ 52,116	49,645
HTM securities: Amortized cost, total	23,564	23,310
Fair Value
AFS debt securities: Fair value, total	50,811	48,837
HTM securities: Fair value, total	$ 22,597	22,792
Average Yield
AFS debt securities: Annualized average yield, total	1.60%
HTM securities: Annualized average yield, total	2.20%
U.S. Treasury Securities
Amortized Cost
AFS debt securities: Amortized cost, due within 1 year	$ 6,153
AFS debt securities: Amortized cost, after 1 year through 5 years	19,385
AFS debt securities: Amortized cost, after 5 years through 10 years	4,494
AFS debt securities: Amortized cost, total	30,032	26,842
HTM securities: Amortized cost, due within 1 year	2,027
HTM securities: Amortized cost, after 1 year through 5 years	3,952
HTM securities: Amortized cost, after 5 year through 10 years	5,112
HTM securities: Amortized cost, after 10 years	726
HTM securities: Amortized cost, total	11,817	11,424
Fair Value
AFS debt securities: Fair value, due within 1 year	6,132
AFS debt securities: Fair value, after 1 year through 5 years	18,906
AFS debt securities: Fair value, after 5 years through 10 years	4,161
AFS debt securities: Fair value, total	29,199	26,253
HTM securities: Fair value, due within 1 year	2,012
HTM securities: Fair value, after 1 year through 5 years	3,871
HTM securities: Fair value, after 5 years through 10 years	4,807
HTM securities: Fair value, after 10 years	637
HTM securities: Fair value, total	$ 11,327	11,119
Average Yield
AFS debt securities: Annualized average yield, due within 1 year	0.90%
AFS debt securities: Annualized average yield, after 1 year through 5 years	1.60%
AFS debt securities: Annualized average yield, after 5 years through 10 years	1.40%
HTM securities: Annualized average yield, due within 1 year	1.20%
HTM securities: Annualized average yield, after 1 years through 5 years	1.80%
HTM securities: Annualized average yield, after 5 years through 10 years	1.90%
HTM securities: Annualized average yield, after 10 year	2.30%
U.S. Agency Securities
Amortized Cost
AFS debt securities: Amortized cost, due within 1 year	$ 43
AFS debt securities: Amortized cost, after 1 year through 5 years	1,899
AFS debt securities: Amortized cost, after 5 years through 10 years	1,555
AFS debt securities: Amortized cost, after 10 years	18,587
AFS debt securities: Amortized cost, total	22,084	22,803
HTM securities: Amortized cost, after 5 year through 10 years	34
HTM securities: Amortized cost, after 10 years	11,713
HTM securities: Amortized cost, total	11,747	11,886
Fair Value
AFS debt securities: Fair value, due within 1 year	42
AFS debt securities: Fair value, after 1 year through 5 years	1,883
AFS debt securities: Fair value, after 5 years through 10 years	1,506
AFS debt securities: Fair value, after 10 years	18,181
AFS debt securities: Fair value, total	21,612	22,584
HTM securities: Fair value, after 5 years through 10 years	33
HTM securities: Fair value, after 10 years	11,237
HTM securities: Fair value, total	$ 11,270	11,673
Average Yield
AFS debt securities: Annualized average yield, due within 1 year	1.10%
AFS debt securities: Annualized average yield, after 1 year through 5 years	1.00%
AFS debt securities: Annualized average yield, after 5 years through 10 years	1.80%
AFS debt securities: Annualized average yield, after 10 years	2.00%
HTM securities: Annualized average yield, after 5 years through 10 years	1.90%
HTM securities: Annualized average yield, after 10 year	2.60%
Corporate and Other Debt
Amortized Cost
AFS debt securities: Amortized cost, total	$ 6,029	6,414
HTM securities: Amortized cost, total	328	289
Fair Value
AFS debt securities: Fair value, total	5,938	6,361
HTM securities: Fair value, total	$ 322	289
Average Yield
AFS debt securities: Annualized average yield, total	1.60%
HTM securities: Annualized average yield, total	3.80%
CMBS: Agency
Amortized Cost
AFS debt securities: Amortized cost, due within 1 year	$ 19
AFS debt securities: Amortized cost, after 1 year through 5 years	431
AFS debt securities: Amortized cost, after 5 years through 10 years	47
AFS debt securities: Amortized cost, after 10 years	805
AFS debt securities: Amortized cost, total	1,302	1,370
Fair Value
AFS debt securities: Fair value, due within 1 year	19
AFS debt securities: Fair value, after 1 year through 5 years	430
AFS debt securities: Fair value, after 5 years through 10 years	47
AFS debt securities: Fair value, after 10 years	749
AFS debt securities: Fair value, total	$ 1,245	1,323
Average Yield
AFS debt securities: Annualized average yield, due within 1 year	1.30%
AFS debt securities: Annualized average yield, after 1 year through 5 years	1.30%
AFS debt securities: Annualized average yield, after 5 years through 10 years	1.20%
AFS debt securities: Annualized average yield, after 10 years	1.60%
CMBS: Non-Agency
Amortized Cost
AFS debt securities: Amortized cost, after 5 years through 10 years	$ 36
AFS debt securities: Amortized cost, after 10 years	821
AFS debt securities: Amortized cost, total	857	1,102
HTM securities: Amortized cost, after 1 year through 5 years	92
HTM securities: Amortized cost, after 5 year through 10 years	217
HTM securities: Amortized cost, after 10 years	19
HTM securities: Amortized cost, total	328	289
Fair Value
AFS debt securities: Fair value, after 5 years through 10 years	35
AFS debt securities: Fair value, after 10 years	807
AFS debt securities: Fair value, total	842	1,094
HTM securities: Fair value, after 1 year through 5 years	92
HTM securities: Fair value, after 5 years through 10 years	212
HTM securities: Fair value, after 10 years	18
HTM securities: Fair value, total	$ 322	289
Average Yield
AFS debt securities: Annualized average yield, after 5 years through 10 years	2.50%
AFS debt securities: Annualized average yield, after 10 years	1.90%
HTM securities: Annualized average yield, after 1 years through 5 years	3.60%
HTM securities: Annualized average yield, after 5 years through 10 years	3.90%
HTM securities: Annualized average yield, after 10 year	4.10%
Corporate Bonds
Amortized Cost
AFS debt securities: Amortized cost, due within 1 year	$ 97
AFS debt securities: Amortized cost, after 1 year through 5 years	1,175
AFS debt securities: Amortized cost, after 5 years through 10 years	74
AFS debt securities: Amortized cost, total	1,346	1,379
Fair Value
AFS debt securities: Fair value, due within 1 year	97
AFS debt securities: Fair value, after 1 year through 5 years	1,150
AFS debt securities: Fair value, after 5 years through 10 years	71
AFS debt securities: Fair value, total	$ 1,318	1,372
Average Yield
AFS debt securities: Annualized average yield, due within 1 year	1.60%
AFS debt securities: Annualized average yield, after 1 year through 5 years	2.40%
AFS debt securities: Annualized average yield, after 5 years through 10 years	2.50%
CLO
Amortized Cost
AFS debt securities: Amortized cost, after 5 years through 10 years	$ 153
AFS debt securities: Amortized cost, after 10 years	198
AFS debt securities: Amortized cost, total	351	398
Fair Value
AFS debt securities: Fair value, after 5 years through 10 years	153
AFS debt securities: Fair value, after 10 years	199
AFS debt securities: Fair value, total	$ 352	399
Average Yield
AFS debt securities: Annualized average yield, after 5 years through 10 years	1.50%
AFS debt securities: Annualized average yield, after 10 years	2.40%
FFELP Student Loan ABS
Amortized Cost
AFS debt securities: Amortized cost, after 1 year through 5 years	$ 48
AFS debt securities: Amortized cost, after 5 years through 10 years	390
AFS debt securities: Amortized cost, after 10 years	1,735
AFS debt securities: Amortized cost, total	2,173	2,165
Fair Value
AFS debt securities: Fair value, after 1 year through 5 years	47
AFS debt securities: Fair value, after 5 years through 10 years	388
AFS debt securities: Fair value, after 10 years	1,746
AFS debt securities: Fair value, total	$ 2,181	$ 2,173
Average Yield
AFS debt securities: Annualized average yield, after 1 year through 5 years	0.80%
AFS debt securities: Annualized average yield, after 5 years through 10 years	0.80%
AFS debt securities: Annualized average yield, after 10 years	1.10%