Investments (details) - Derivatives (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Mar. 31, 2013	Dec. 31, 2012
Derivative
Net realized investment gain (loss)	$ 167,000,000	[1]	$ 4,000,000	[1]	$ 177,000,000	[1]	$ 14,000,000	[1]
Futures [Member] | U.S. Treasury notes contracts [Member]
Derivative
Notional value of open contracts	0				0				2,000,000,000	800,000,000
Net realized investment gain (loss)	134,000,000		(13,000,000)		115,000,000		(7,000,000)
Futures [Member] | U.S. Treasury notes contracts [Member] | Maxiumum [Member]
Derivative
Notional value of open contracts	$ 2,700,000,000				$ 2,700,000,000

[1] Total other-than-temporary impairment (OTTI) gains (losses) were $(1) million and $11 million for the three months ended June 30, 2013 and 2012, respectively, and $(1) million and $11 million for the six months ended June 30, 2013 and 2012, respectively. Of total OTTI, credit losses of $(2) million and $(4) million for the three months ended June 30, 2013 and 2012, respectively, and $(7) million and $(8) million for the six months ended June 30, 2013 and 2012, respectively, were recognized in net realized investment gains. In addition, unrealized gains from other changes in total OTTI of $1 million and $15 million for the three months ended June 30, 2013 and 2012, respectively, and $6 million and $19 million for the six months ended June 30, 2013 and 2012, respectively, were recognized in other comprehensive income as part of change in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income.