Investment Securities - Narrative (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			$ 3,000,000	$ 1,000,000	$ 11,000,000
Pledged securities not separately reported	$ 46,000,000,000	$ 41,000,000,000	46,000,000,000	41,000,000,000
Available for sale securities transferred to held to maturity	$ 4,900,000,000	$ 7,100,000,000
Unrealized gain			87,000,000	89,000,000
Minimum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Remaining life of transferred securities	7 years
Maximum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Remaining life of transferred securities	49 years
Agency Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			0	0	0
Federal family education loan program
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			$ 0	0	0
Average term on asset backed securities			4 years 1 month 6 days
Available-for-sale Securities, Downgraded by Ratings Agency	$ 1,700,000,000
Available-for-sale Securities, Credit Watch	$ 2,200,000,000		$ 2,200,000,000
Asset-backed securities, student loans
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			0	0	0
Less than maximum credit exposure			200,000,000
Non-U.S. debt securities, mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			$ 2,000,000	1,000,000	1,000,000
Non-U.S. debt securities, mortgage-backed securities | Minimum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Additional price declines forecast, percent			3.00%
Non-U.S. debt securities, mortgage-backed securities | Maximum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Additional price declines forecast, percent			23.00%
State and political subdivisions
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			$ 0	0	0
U.S. Non-Agency Residential Mortgage-Backed Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			0	0	0
U.S. Non-Agency Commercial Mortgage Backed Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Net impairment losses			1,000,000	$ 0	$ 10,000,000
Gross pre-tax unrealized losses			$ 820,000,000
Number of securities in loss position | security			1,727