Goodwill and Other Intangibles - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill acquired during period	$ 8	$ 8
Amortizable intangible assets related to property and casualty insurance acquisitions	54	54	$ 26
Accumulated amortization	39	39	30
Amortization of intangible assets		$ 9	$ 8	$ 8
Weighted average useful life of finite-lived intangible assets acquired		7 years
Future amortization of intangibles in next year	12	$ 12
Future amortization of intangibles in year two	12	12
Future amortization of intangibles in year three	6	6
Future amortization of intangibles in year four	4	4
Future amortization of intangibles in year five	4	4
Future amortization of intangibles after year five	$ 16	$ 16