Supplemental Cash Flow Information - Activities resulting from management of proceeds (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Net change in proceeds managed
Net change in fixed income securities	$ 80	$ 175
Net change in short-term investments	(709)	(454)
Operating cash flow used	(629)	(279)
Change in Liabilities for Collateral [Roll Forward]
Liabilities for collateral, beginning of period	(1,458)	(1,124)
Liabilities for collateral, end of period	(2,087)	(1,403)
Operating cash flow provided	$ 629	$ 279