Geographic Regions (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues	$ 296	$ 286	$ 253	$ 252	$ 179	$ 180	$ 179	$ 180	$ 1,087	$ 718	$ 755
Pretax income	$ 72	$ 85	$ 52	$ 66	$ 20	$ 70	$ 65	$ 57	275	212	252
United States [Member]
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues									779	440	442
Pretax income									9	16	111
Outside the United States [Member]
Segment Revenues and Pretax Income (Loss) by Geographic Location [Line Items]
Revenues									308	278	313
Pretax income									$ 266	$ 196	$ 141