Reinsurance (Voluntary Reinsurance) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Effects of Reinsurance [Line Items]
Total voluntary reinsurance outstanding balance	$ 3,727
A- to A++
Effects of Reinsurance [Line Items]
Total voluntary reinsurance outstanding balance	2,820
B- to B++
Effects of Reinsurance [Line Items]
Total voluntary reinsurance outstanding balance	904
Insolvent
Effects of Reinsurance [Line Items]
Total voluntary reinsurance outstanding balance	$ 3