Condensed Financial Statements - Other Investments (Details) - BYD Company Limited common stock [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	$ 1,185	$ 1,238
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes	953	1,006
Parent Company [Member]
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	1,185	1,238
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes	$ 953	$ 1,006