Investments - Rollforward of credit loss allowance for mortgage loans (Details) - Mortgage loans on real estate - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ (3)
Net increases related to credit losses	(39)	$ 0	$ 0
Reduction of allowance related to sales	17
Write-offs	0
Ending balance	(67)	(3)
Cumulative effect of change in accounting principle
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ (42)
Ending balance		$ (42)