Investments - Net appreciation (decline) recognized in net income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Realized capital gains and losses by asset type
Net appreciation (decline) recognized in net income	$ 312	$ 156	$ 136	$ 845
Equity securities
Realized capital gains and losses by asset type
Net appreciation (decline) recognized in net income	184	107	116	736
Limited partnership interests
Realized capital gains and losses by asset type
Net appreciation (decline) recognized in net income	$ 128	$ 49	$ 20	$ 109