Fair Value - Schedule of Availability of Significant Unobservable Inputs by Balance Sheet Classification (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets:
Investment securities available for sale	$ 80,097	$ 94,913
Asset-backed securities, student loans
Assets:
Investment securities available for sale	7,644	12,460
Asset-backed securities, other
Assets:
Investment securities available for sale	1,955	4,145
Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	7,916	9,606
Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	3,198	3,226
Non-U.S. debt securities, other
Assets:
Investment securities available for sale	5,002	5,428
State and political subdivisions
Assets:
Investment securities available for sale	9,974	10,820
Collateralized mortgage obligations
Assets:
Investment securities available for sale	3,299	5,339
Other U.S. debt securities
Assets:
Investment securities available for sale	2,907	4,109
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Assets, fair value disclosure	2,926	5,447
Liabilities:
Liabilities, fair value disclosure	22	83
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts, liabilities	22	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	21	81
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	230	259
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	1,943	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	0
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	277	295
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale	263	371
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	35	38
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	148	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	94	178
Liabilities:
Liabilities, fair value disclosure	22	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	22	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	21	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	38	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	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	2,832	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	230	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	1,905	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	0
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	277	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	263	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	0	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	148	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