Investments - Valuation changes included in net income for investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 1,222	$ (12)
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Total	1,073	(261)
Limited partnership interests
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 149	$ 249