Investment Securities (Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investment Securities [Abstract]
Available for sale securities: Less than 12 months Fair Value	$ 29,156	$ 38,165
Available for sale securities: Less than 12 months Unrealized Losses	212	341
Available for sale securities: 12 months or longer Fair Value	12,921	6,644
Available for sale securities: 12 months or longer Unrealized Losses	226	91
Available for sale securities: Total Fair Value	42,077	44,809
Available for sale securities: Total Unrealized Losses	438	432
Held to maturity securities: Less than 12 months Fair Value	52,185	25,168
Held to maturity securities: Less than 12 months Unrealized Losses	1,095	276
Held to maturity securities: 12 months or longer Fair Value		1,842
Held to maturity securities: 12 months or longer Unrealized Losses		40
Held to maturity securities: Total Fair Value	52,185	27,010
Held to maturity securities: Total Unrealized Losses	1,095	316
Total securities with unrealized losses: Less than 12 months Fair Value	81,341	63,333
Total securities with unrealized losses: Less than 12 months Unrealized Losses	1,307	617
Total securities with unrealized losses: 12 months or longer Fair Value	12,921	8,486
Total securities with unrealized losses: 12 months or longer Unrealized Losses	226	131
Total securities with unrealized losses: Total Fair Value	94,262	71,819
Total securities with unrealized losses: Total Unrealized Losses	$ 1,533	$ 748