Fair Value - Fair Value Inputs, Assets and Liabilities, Quantitative Information (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	$ 85,308	$ 94,913
Asset-backed securities, student loans
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	9,139	12,460
Asset-backed securities, credit cards
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	1,569	3,053
Asset-backed securities, other
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	3,005	4,145
State and political subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	10,449	10,820
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, fair value disclosure	4,041	5,447
Liabilities, fair value disclosure	50	83
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative instruments, foreign exchange contracts, assets	60	81
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	234	259
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	2,933	3,780
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	$ 36	$ 38
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Discounted cash flows | Derivative instruments, liabilities | Weighted average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Participant redemptions	0.00%	5.20%
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Discounted cash flows | Asset-backed securities, other | Weighted average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Credit spread	0.10%	0.20%
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Discounted cash flows | State and political subdivisions | Weighted average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Credit spread	2.20%	2.10%
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Option model | Derivative instruments, liabilities | Weighted average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility	12.30%	9.00%
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Option model | Derivative instruments, assets | Weighted average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility	12.00%	9.10%
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, fair value disclosure	$ 142	$ 178
Liabilities, fair value disclosure	50	83
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Derivative instruments, liabilities
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
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
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	47	59
Significant Unobservable Inputs Readily Available | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Investment securities available for sale	$ 35	$ 38