Investments, Aggregate Contractual or Notional Amounts and Estimated Fair Values Related to Derivative Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
With Hedge Designation [Member] | Interest Rate Swaps [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	$ 675	$ 715
Liability, estimated fair value	(26)	(8)
Without Hedge Designation [Member] | Interest Rate Swaps [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	100
Liability, estimated fair value	(3)
Without Hedge Designation [Member] | Options [Member] | Purchased [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	135	57
Asset, estimated fair value	3	1
Without Hedge Designation [Member] | Options [Member] | Written [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount		100
Liability, estimated fair value		(1)
Without Hedge Designation [Member] | Embedded Derivative on Funds Withheld Liability [Member]
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/notional amount	190	182
Liability, estimated fair value	$ (19)	$ (7)