Income Taxes - Additional Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Taxes Other Information [Line Items]
Deferred Tax Assets, Valuation Allowance	$ 98		$ 102
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%		35.00%		35.00%
Income Tax Expense (Benefit)	493	[1]	322	[1]	812	[1]
Effective Income Tax Rate Reconciliation, Percent	21.80%		19.30%		29.30%
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	148
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	20		17
Unrecognized Tax Benefits, Interest on Income Taxes Expense	3		(1)
Significant (Increase) Decrease in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound	$ 52

[1] Amortization expense related to qualified affordable housing investment costs is recognized in provision for income taxes for each of the periods presented as allowed by an accounting standard adopted in 2014. Prior to 2014, these amounts were recognized in other noninterest expense.