Supplemental Cash Flow Information - Activities resulting from management of proceeds (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Net change in proceeds managed
Net change in short-term investments	$ (583)	$ 336
Operating cash flow (used) provided	(583)	336
Net change in cash	2	(8)
Net change in proceeds managed	(581)	328
Change in Liabilities for Collateral [Roll Forward]
Liabilities for collateral, beginning of period	(914)	(1,298)
Liabilities for collateral, end of period	(1,495)	(970)
Operating cash flow provided (used)	$ 581	$ (328)