Goodwill and Other Intangibles - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill acquired during period	$ 8			$ 8
Amortizable intangible assets related to property and casualty insurance acquisitions		$ 34	$ 43
Accumulated amortization		62	50
Amortization of intangible assets		$ 12	$ 11	$ 9
Weighted average useful life of finite-lived intangible assets acquired		3 years
Future amortization of intangibles in next year		$ 6
Future amortization of intangibles in year two		4
Future amortization of intangibles in year three		4
Future amortization of intangibles in year four		4
Future amortization of intangibles in year five		4
Future amortization of intangibles after year five		$ 12