Supplemental Cash Flow Information - Activities resulting from management of proceeds (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Net change in proceeds managed
Net change in fixed income securities	$ 80	$ 122
Net change in short-term investments	(493)	(663)
Operating cash flow used	(413)	(541)
Change in Liabilities for Collateral [Roll Forward]
Liabilities for collateral, beginning of period	(1,458)	(1,124)
Liabilities for collateral, end of period	(1,871)	(1,665)
Operating cash flow provided	$ 413	$ 541