Other Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-lived intangible assets	$ 18	$ 16
Indefinite-lived intangible assets	63	59
Intangible Assets, Gross (Excluding Goodwill)	81	75
Accumulated amortization	9	6
Syndicate capacity
Indefinite-lived intangible assets	47	43
Agency force
Indefinite-lived intangible assets	$ 16	16
Trade name
Economic useful life measured in years	8 years
Finite-lived intangible assets	$ 7	6
Accumulated amortization	$ 5	3
Distribution channel
Economic useful life measured in years	15 years
Finite-lived intangible assets	$ 11	10
Accumulated amortization	$ 4	$ 3