Condensed Financial Statements - Other Investments (Details) - BYD Company Limited common stock [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	$ 1,238	$ 881
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes	1,000	649
Parent Company [Member]
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]
Available-for-sale Securities, Equity Securities	1,200	881
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes	$ 1,000	$ 649