Investments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Investment Holdings [Line Items]      
Other than temporary impairment loss on investments $ 0 $ 0  
Affordable housing project equity method investments 197   201
Contingent liabilities related to affordable housing project equity method investments 32   38
Community Reinvestment Act [Member] | Other Assets [Member]      
Investment Holdings [Line Items]      
Equity method investments 312   325
Community Reinvestment Act [Member] | Other Liabilities [Member]      
Investment Holdings [Line Items]      
Contingent liabilities related to equity method investments $ 46   $ 51