Fair Value - Schedule of Availability of Significant Unobservable Inputs by Balance Sheet Classification (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Assets:
Investment securities available for sale	$ 85,308	$ 94,913
Asset-backed securities, student loans
Assets:
Investment securities available for sale	9,139	12,460
Asset-backed securities, credit cards
Assets:
Investment securities available for sale	1,569	3,053
Asset-backed securities, other
Assets:
Investment securities available for sale	3,005	4,145
Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	8,329	9,606
Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	2,933	3,226
Non-U.S. debt securities, other
Assets:
Investment securities available for sale	5,118	5,428
State and political subdivisions
Assets:
Investment securities available for sale	10,449	10,820
Collateralized mortgage obligations
Assets:
Investment securities available for sale	3,984	5,339
Other U.S. debt securities
Assets:
Investment securities available for sale	3,336	4,109
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Assets, fair value disclosure	4,041	5,447
Liabilities:
Liabilities, fair value disclosure	50	83
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts, liabilities	50	74
Derivative instruments, other, liabilities		9
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts, assets	60	81
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	234	259
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	2,933	3,780
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	97
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	193	295
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale	264	371
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	36	38
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	215	614
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S. debt securities
Assets:
Investment securities available for sale	9	9
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Assets, fair value disclosure	142	178
Liabilities:
Liabilities, fair value disclosure	50	83
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts, liabilities	50	74
Derivative instruments, other, liabilities	0	9
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts, assets	60	81
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	0	0
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	47	59
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	0
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	$ 0	0
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale		0
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	$ 35	38
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	0	0
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S. debt securities
Assets:
Investment securities available for sale	0	0
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Assets, fair value disclosure	3,899	5,269
Liabilities:
Liabilities, fair value disclosure	0	0
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts, liabilities	0	0
Derivative instruments, other, liabilities		0
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts, assets	0	0
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	234	259
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	2,886	3,721
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	97
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	193	295
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale	264	371
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	1	0
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	215	614
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S. debt securities
Assets:
Investment securities available for sale	$ 9	$ 9