Shareholders' Equity - Regulatory Requirements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statutory Accounting Practices [Line Items]
Combined statutory net income	$ 2,800
Estimated minimum statutory surplus required by regulators	5,841
Investments on deposit with regulatory bodies	672
Estimated maximum dividend distributions permitted in 2020 without prior regulatory approval	366
Insurance and HMO
Statutory Accounting Practices [Line Items]
Combined statutory capital and surplus	11,000	$ 10,100
Dividends paid	$ 2,400