Investments - Carrying Values of Other Long-Term Investments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Other long-term investments	$ 2,735	$ 2,403
Real estate investments
Schedule of Investments [Line Items]
Other long-term investments	848	788
Securities partnerships
Schedule of Investments [Line Items]
Other long-term investments	1,517	1,409
Other
Schedule of Investments [Line Items]
Other long-term investments	$ 370	$ 206