Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net Investment Income:
Investment income, before expense	$ 1,015	$ 251	$ 1,760	$ 533
Investment expense	(41)	(31)	(78)	(67)
Net investment income	974	220	1,682	466
Fixed income securities
Net Investment Income:
Investment income, before expense	290	306	591	604
Equity securities
Net Investment Income:
Investment income, before expense	13	21	27	31
Mortgage loans
Net Investment Income:
Investment income, before expense	12	8	22	17
Limited partnership interests
Net Investment Income:
Investment income, before expense	651	(117)	1,029	(194)
Short-term investments
Net Investment Income:
Investment income, before expense	1	2	2	13
Other
Net Investment Income:
Investment income, before expense	$ 48	$ 31	$ 89	$ 62