Goodwill and Other Intangibles - Changes in the carrying value of goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Changes in the carrying value of goodwill by reporting segment
Goodwill, Beginning balance	$ 207	$ 207	$ 207	$ 207	$ 199
Goodwill, acquisition of subsidiary	8	8
Goodwill, Ending balance	207	207
Property and Casualty
Changes in the carrying value of goodwill by reporting segment
Goodwill, Beginning balance	176	176	176	176	168
Goodwill, acquisition of subsidiary		8
Goodwill, Ending balance	176	176
Annuity
Changes in the carrying value of goodwill by reporting segment
Goodwill, Beginning balance	31	31	$ 31	$ 31	$ 31
Goodwill, acquisition of subsidiary		0
Goodwill, Ending balance	$ 31	$ 31