Equity Method Investments (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Equity method investment difference between carrying amount and underlying equity	$ 1,210
Equity method investment difference between carrying amount and underlying equity, portion related to goodwill which is not being amortized	553
Equity method investments	3,827	$ 3,622
Dividends and partnership distributions received from equity method investees	291	113	$ 170
Centennial
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 35	$ 37
Percent of debt outstanding	50.00%
Centennial | Financial Guarantee
Schedule of Equity Method Investments [Line Items]
Maximum potential undiscounted payments	$ 29