Fair Value - Schedule of Availability of Significant Unobservable Inputs by Balance Sheet Classification (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Assets:
Investment securities available for sale	$ 70,070	$ 94,913
Asset-backed securities, student loans
Assets:
Investment securities available for sale	7,176	12,460
Asset-backed securities, other
Assets:
Investment securities available for sale	1,764	4,145
Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	7,071	9,606
Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	3,267	3,226
Non-U.S. debt securities, other
Assets:
Investment securities available for sale	4,834	5,428
State and political subdivisions
Assets:
Investment securities available for sale	9,746	10,820
Collateralized mortgage obligations
Assets:
Investment securities available for sale	2,987	5,339
Other U.S. debt securities
Assets:
Investment securities available for sale	2,624	4,109
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	2,469	5,447
Liabilities:
Total	5	83
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts	5	74
Derivative instruments, other		9
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts	5	81
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	189	259
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	1,764	3,780
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	174	295
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale	255	371
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	33	38
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	39	614
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S. debt securities
Assets:
Investment securities available for sale	10	9
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	66	178
Liabilities:
Total	5	83
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts	5	74
Derivative instruments, other	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	5	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	28	59
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	33	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:
Total	2,403	5,269
Liabilities:
Total	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	0	0
Derivative instruments, other		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	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	189	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	1,736	3,721
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	174	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	255	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	39	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	$ 10	$ 9