Investments - Net investment income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Investment Income:
Investment income, before expense	$ 719	$ 851
Investment expense	(71)	(65)
Net investment income	648	786
Fixed income securities
Net Investment Income:
Investment income, before expense	538	508
Equity securities
Net Investment Income:
Investment income, before expense	30	34
Mortgage loans
Net Investment Income:
Investment income, before expense	53	51
Limited partnership interests
Net Investment Income:
Investment income, before expense	9	180
Short-term investments
Net Investment Income:
Investment income, before expense	26	12
Other
Net Investment Income:
Investment income, before expense	$ 63	$ 66