Fair Value Measurements - Fair Value Option (Details) - USD ($) $ in Millions	3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	May 31, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value, Option, Fixed Maturity Securities	$ 14		$ 14			$ 32
Residential Mortgage Backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value, Option, Fixed Maturity Securities	14		14			$ 32
Fair Value, Option, Changes in Fair Value, Gain (Loss)	$ 0	$ 0	$ 0	$ 0	$ 2