Condensed Financial Statements - Other Investments (Details) - BYD Company Limited common stock [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	$ 1,435	$ 1,961
Parent Company [Member]
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	1,435	1,961
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax	$ 1,203	$ 1,729