Shareholders' Equity - Regulatory Requirements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statutory Accounting Practices [Line Items]
Combined statutory net income	$ 3,667	$ 2,842
Estimated minimum statutory surplus required by regulators	5,395
Investments on deposit with regulatory bodies	712
Estimated maximum dividend distributions permitted in 2021 without prior regulatory approval	2,900
Insurance and HMO
Statutory Accounting Practices [Line Items]
Combined statutory capital and surplus	13,238	$ 10,975	$ 10,084
Dividends paid	$ 3,100