Investments (Schedule of Fair Value of Securities in a Continuous Unrealized Loss Position for Less Than 12 Months and More Than 12 Months) (Details) (Residential Mortgage-Backed Securities - Agency [Member], USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
securities
Residential Mortgage-Backed Securities - Agency [Member]
 
Investment Holdings [Line Items]  
Available-for-sale investment securities, number of securities in a loss position (in securities) 8
Available-for-sale investment securities, continuous unrealized loss position, less than 12 months, fair value $ 97
Available-for-sale investment securities, continuous unrealized loss position, less than 12 months, unrealized losses 0
Available-for-sale investment securities, continuous unrealized loss position, more than 12 months, fair value 225
Available-for-sale investment securities, continuous unrealized loss position, more than 12 months, unrealized losses $ (1)