Goodwill and Other Intangibles - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the goodwill balance during the period			$ 0
Goodwill	$ 199,000,000		199,000,000		$ 199,000,000
Amortizable intangible assets related to property and casualty insurance acquisitions	31,000,000		31,000,000		26,000,000
Accumulated amortization	37,000,000		37,000,000		$ 30,000,000
Amortization of intangible assets	$ 3,000,000	$ 2,000,000	$ 7,000,000	$ 6,000,000