Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Investments related to 2012 contract conversion	$ 524	$ 537
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	2 years 4 months 24 days
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	6 years 1 month 6 days
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Weighted average duration of securities	1 year 1 month 6 days