Fair Value - Schedule of Availability of Significant Unobservable Inputs by Balance Sheet Classification (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Assets:
Investment securities available-for-sale	$ 72,735	$ 70,070
Asset-backed securities, student loans
Assets:
Investment securities available-for-sale	6,954	7,176
Asset-backed securities, other
Assets:
Investment securities available-for-sale	1,710	1,764
Non-U.S. debt securities, asset-backed securities
Assets:
Investment securities available-for-sale	2,668	3,267
Non-U.S. debt securities, other
Assets:
Investment securities available-for-sale	5,374	4,834
State and political subdivisions
Assets:
Investment securities available-for-sale	10,603	9,746
Collateralized mortgage obligations
Assets:
Investment securities available-for-sale	2,741	2,987
Other U.S. debt securities
Assets:
Investment securities available-for-sale	2,390	2,624
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Assets:
Total	2,398	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	25
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Assets:
Investment securities available-for-sale	190	189
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Assets:
Investment securities available-for-sale	1,710	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	111	174
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Assets:
Investment securities available-for-sale	261	255
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Assets:
Investment securities available-for-sale	33	33
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Assets:
Investment securities available-for-sale	68	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	55	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	22	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	33	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	2,343	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	25
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	190	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	1,688	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	111	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	261	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	$ 68	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