Supplemental Cash Flow Information - Activities resulting from management of proceeds (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net change in proceeds managed
Net change in fixed income securities	$ 60	$ 32
Net change in short-term investments	(575)	55
Operating cash flow (used) provided	(515)	87
Change in Liabilities for Collateral [Roll Forward]
Liabilities for collateral, beginning of period	(1,458)	(1,124)
Liabilities for collateral, end of period	(1,973)	(1,037)
Operating cash flow provided (used)	$ 515	$ (87)