Debt and Interest Expense - Outstanding Debt Table (Detail) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Total debt at face value		$ 17,640	$ 16,687
Net unamortized discounts and premiums (1)	[1]	(1,603)	(1,616)
Total borrowings		16,037	15,071
Capital lease obligation		21	21
Less short-term debt		33	0
Debt Instrument [Line Items]
Total long-term debt (2)	[2]	16,025	15,092
Partnership [Member]
Debt Instrument [Line Items]
Total long-term debt (2)		$ 2,700	$ 2,400

[1] Unamortized discounts and premiums are amortized over the term of the related debt.

[2] Includes WES debt of $2.7 billion at June 30, 2015, and $2.4 billion at December 31, 2014.