Investments and Cash - Roll Forward of Credit Losses in the Investment Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Roll Forward of Credit Losses in the Investment Portfolio
Credit losses, beginning of period	$ 106	$ 85	$ 124	$ 80
Additions for credit losses on securities for which an other-than-temporary-impairment was not previously recognized	0	9	0	10
Reductions for securities sold and other settlement during the period	(7)	(12)	(28)	(12)
Additions for credit losses on securities for which an other-than-temporary-impairment was previously recognized	5	2	8	6
Credit losses, end of period	$ 104	$ 84	$ 104	$ 84