Investments - Other Segments and Holding Company (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Investments	$ 11,480		$ 8,913
Other Segments and Holding Company
Schedule of Investments [Line Items]
Investments	554		674
Unrealized gains (losses) that relate to equity securities still held	58	$ (312)
Other Segments and Holding Company | Equity method investments
Schedule of Investments [Line Items]
Investments	108		120
Other Segments and Holding Company | Held to maturity debt investments measured at amortized cost
Schedule of Investments [Line Items]
Investments	20		20
Other Segments and Holding Company | Other investments measured at fair value
Schedule of Investments [Line Items]
Investments	$ 426		$ 534