Fair Value Measurement and Fair Value of Financial Instruments - Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	$ 14,336
Other liabilities	2,023	$ 1,897
Other debt securities, Direct bank purchase bonds
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	$ 1,572
Other debt securities, Direct bank purchase bonds | Minimum | Return on equity
Significant unobservable inputs, Level 3 assets
Market-required return on capital (as a percent)	8.00%
Probability of default (as a percent)	0.00%
Loss severity (as a percent)	10.00%
Other debt securities, Direct bank purchase bonds | Maximum | Return on equity
Significant unobservable inputs, Level 3 assets
Market-required return on capital (as a percent)	10.00%
Probability of default (as a percent)	25.00%
Loss severity (as a percent)	60.00%
Other debt securities, Direct bank purchase bonds | Weighted Average | Return on equity
Significant unobservable inputs, Level 3 assets
Market-required return on capital (as a percent)	9.90%
Probability of default (as a percent)	0.50%
Loss severity (as a percent)	30.60%
FDIC clawback liability | Minimum | Discounted cash flow
Significant unobservable inputs, Level 3 assets
Probability of default (as a percent)	0.10%
Loss severity (as a percent)	0.00%
FDIC clawback liability | Maximum | Discounted cash flow
Significant unobservable inputs, Level 3 assets
Probability of default (as a percent)	100.00%
Loss severity (as a percent)	100.00%
FDIC clawback liability | Weighted Average | Discounted cash flow
Significant unobservable inputs, Level 3 assets
Probability of default (as a percent)	53.10%
Loss severity (as a percent)	43.50%
Fair Value, Measurements, Recurring
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	$ 14,344	13,724
Fair Value, Measurements, Recurring | Other debt securities, Direct bank purchase bonds
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	1,572	1,741
Fair Value, Measurements, Recurring | Level 3
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	1,603	1,790
Fair Value, Measurements, Recurring | Level 3 | Other debt securities, Direct bank purchase bonds
Significant unobservable inputs, Level 3 assets
Available-for-sale Securities, Debt Securities	1,572	$ 1,741
Fair Value, Measurements, Recurring | FDIC clawback liability
Significant unobservable inputs, Level 3 assets
Other liabilities	$ 112