Fair Value - Schedule of Availability of Significant Unobservable Inputs by Balance Sheet Classification (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Assets:
Investment securities available for sale	$ 71,086	$ 70,070
Asset-backed securities, student loans
Assets:
Investment securities available for sale	6,817	7,176
Asset-backed securities, other
Assets:
Investment securities available for sale	1,813	1,764
Non-U.S. debt securities, mortgage-backed securities
Assets:
Investment securities available for sale	7,612	7,071
Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	2,704	3,267
Non-U.S. debt securities, other
Assets:
Investment securities available for sale	5,009	4,834
State and political subdivisions
Assets:
Investment securities available for sale	10,026	9,746
Collateralized mortgage obligations
Assets:
Investment securities available for sale	2,938	2,987
Other U.S. debt securities
Assets:
Investment securities available for sale	2,231	2,624
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	2,835	2,469
Liabilities:
Total		5
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts		5
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts		5
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized Mortgage Backed Securities
Assets:
Investment securities available for sale	300
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available for sale	186	189
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available for sale	1,813	1,764
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available for sale	127	174
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available for sale	295	255
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available for sale	32	33
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available for sale	82	39
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S. debt securities
Assets:
Investment securities available for sale		10
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	56	66
Liabilities:
Total	0	5
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Liabilities:
Derivative instruments, foreign exchange contracts	0	5
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, assets
Assets:
Derivative instruments, foreign exchange contracts	0	5
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized Mortgage Backed Securities
Assets:
Investment securities available for sale	0
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	24	28
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	32	33
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
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	2,779	2,403
Liabilities:
Total		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
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
Significant Unobservable Inputs Not Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized Mortgage Backed Securities
Assets:
Investment securities available for sale	300
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	186	189
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	1,789	1,736
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	127	174
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	295	255
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	$ 82	39
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