Geographic Regions (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues	$ 406	$ 386	$ 351	$ 318	$ 296	$ 286	$ 253	$ 252	$ 1,461	$ 1,087	$ 718
Pretax income	$ 108	$ 107	$ 93	$ 108	$ 72	$ 85	$ 52	$ 66	416	275	212
United States [Member]
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues									1,033	779	440
Pretax income									28	9	16
Outside the United States [Member]
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues									428	308	278
Pretax income									$ 388	$ 266	$ 196