Contracts Accounted for as Insurance - Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning of period	$ 105	$ 101	$ 106
DAC adjustments related to Radian Asset Acquisition on April 1, 2015	0	0	(2)
Costs deferred during the period:
Costs deferred during the period	23	19	16
Costs amortized during the period	(17)	(15)	(19)
End of period	$ 111	$ 105	$ 101