Goodwill and Other Intangibles - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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
Amortizable intangible assets related to property and casualty insurance acquisitions	36,000,000		26,000,000
Accumulated amortization	32,000,000		$ 30,000,000
Amortization of intangible assets	$ 2,000,000	$ 2,000,000