Investments and Cash - Roll Forward of Credit Losses in the Investment Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Roll Forward of Credit Losses in the Investment Portfolio
Credit losses, beginning of period	$ 104	$ 84	$ 124	$ 80
Additions for credit losses on securities for which an other-than-temporary-impairment was not previously recognized	2	3	2	29
Reductions for securities sold and other settlement during the period	0	0	(28)	(12)
Additions for credit losses on securities for which an other-than-temporary-impairment was previously recognized	0	17	8	7
Credit losses, end of period	$ 106	$ 104	$ 106	$ 104