Supplemental Cash Flow Information - Activities resulting from management of proceeds (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net change in proceeds managed
Net change in fixed income securities	$ 32	$ (17)
Net change in short-term investments	55	(26)
Operating cash flow provided (used)	87	(43)
Change in Liabilities for Collateral [Roll Forward]
Liabilities for collateral, beginning of period	(1,124)	(1,129)
Liabilities for collateral, end of period	(1,037)	(1,172)
Operating cash flow (used) provided	$ (87)	$ 43