Investments (details) - Derivatives (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Derivative
Net realized investment gain (loss)	$ (22,000,000)	[1]	$ (2,000,000)	[1]	$ 155,000,000	[1]	$ 12,000,000	[1]
Futures [Member] | U.S. Treasury notes contracts [Member]
Derivative
Notional value of open contracts	0				0				800,000,000
Net realized investment gain (loss)	$ 0		$ (8,000,000)		$ 115,000,000		$ (15,000,000)

[1] Total other-than-temporary impairment (OTTI) gains (losses) were $0 million and $17 million for the three months ended September 30, 2013 and 2012, respectively, and $(1) million and $28 million for the nine months ended September 30, 2013 and 2012, respectively. Of total OTTI, credit losses of $(3) million for each of the three months ended September 30, 2013 and 2012, and $(10) million and $(11) million for the nine months ended September 30, 2013 and 2012, respectively, were recognized in net realized investment gains (losses). In addition, unrealized gains from other changes in total OTTI of $3 million and $20 million for the three months ended September 30, 2013 and 2012, respectively, and $9 million and $39 million for the nine months ended September 30, 2013 and 2012, respectively, were recognized in other comprehensive income (loss) as part of change in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income.