Investments (details) - Derivatives - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivatives
Net realized investment gains (losses)	[1]	$ 3	$ 79	$ 166
Futures [Member] | U.S. Treasury notes contracts [Member]
Derivatives
Notional value of open contracts		400	350
Net realized investment gains (losses)		$ (5)	$ (1)	$ 115

[1] Total other-than-temporary impairment (OTTI) losses were $(54) million, $(22) million and $(10) million for the years ended December 31, 2015, 2014 and 2013, respectively. Of total OTTI, credit losses of $(52) million, $(26) million and $(15) million for the years ended December 31, 2015, 2014 and 2013, respectively, were recognized in net realized investment gains. In addition, unrealized gains (losses) from other changes in total OTTI of $(2) million, $4 million and $5 million for the years ended December 31, 2015, 2014 and 2013, respectively, were recognized in other comprehensive income (loss) as part of changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income.