Investments - Components of Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Investment Income [Line Items]
Investment income	$ 1,296	$ 1,443	$ 1,535
Less investment expenses	52	53	55
Net investment income	1,244	1,390	1,480
Debt securities
Net Investment Income [Line Items]
Investment income	962	986	1,009
Equity securities
Net Investment Income [Line Items]
Investment income	11	5	28
Commercial mortgage loans
Net Investment Income [Line Items]
Investment income	80	88	78
Policy loans
Net Investment Income [Line Items]
Investment income	64	66	70
Other long-term investments
Net Investment Income [Line Items]
Investment income	127	167	156
Short-term investments and cash
Net Investment Income [Line Items]
Investment income	$ 52	$ 131	$ 194