Other Assets and Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Dividends received from consolidated subsidiaries	$ 558	$ 66	$ 46
Dividends received from affiliates accounted for using the equity method	$ 5	$ 4	$ 24