Quarterly Operating Results (Unaudited) - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Operating Results (Unaudited) [Line Items]
Net investment income									$ 2,132	$ 2,303	$ 2,094
Excluding Alternative Investments
Quarterly Operating Results (Unaudited) [Line Items]
Net investment income	$ 465	$ 511	$ 520	$ 511	$ 545	$ 531	$ 531	$ 516	2,007	2,123
Alternative Investments
Quarterly Operating Results (Unaudited) [Line Items]
Net investment income	$ 83	$ 61	$ (52)	$ 33	$ 48	$ 57	$ 49	$ 26	$ 125	$ 180