Investments and Cash - Investment Portfolio Carrying Value (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 10,818	$ 11,301
Short-term investments, at fair value	729	627
Other invested assets	55	94
Total investment portfolio	$ 10,873	$ 11,395
BIG [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities rated as BIG	10.80%	10.50%
Externally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 8,909	$ 9,443
Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	1,180	1,231
Alternative Investments [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	39	69
Other Investments [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	$ 16	$ 25