Fair Value Measurement and Fair Value of Financial Instruments (Details 3) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Unobservable Input(s) Level 3
Securities available for sale	$ 14,355	$ 13,724
Other liabilities	$ 2,060	1,897
Fdic | Minimum | Discounted cash flow
Unobservable Input(s) Level 3
Probability of default (as a percent)	0.10%
Loss severity (as a percent)	0.00%
Fdic | Maximum | Discounted cash flow
Unobservable Input(s) Level 3
Probability of default (as a percent)	100.00%
Loss severity (as a percent)	100.00%
Fdic | Weighted Average | Discounted cash flow
Unobservable Input(s) Level 3
Probability of default (as a percent)	49.90%
Loss severity (as a percent)	35.90%
Level 3 | Fdic
Unobservable Input(s) Level 3
Other liabilities	$ 110
Other debt securities, Direct bank purchase bonds
Unobservable Input(s) Level 3
Securities available for sale	$ 1,594	$ 1,741
Other debt securities, Direct bank purchase bonds | Minimum | Return on equity
Unobservable Input(s) Level 3
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
Unobservable Input(s) Level 3
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
Unobservable Input(s) Level 3
Market-required return on capital (as a percent)	9.90%
Probability of default (as a percent)	0.50%
Loss severity (as a percent)	30.10%
Other debt securities, Direct bank purchase bonds | Level 3
Unobservable Input(s) Level 3
Securities available for sale	$ 1,594