Debt and Interest Expense - Outstanding Debt Table (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt Disclosure [Abstract]
Total debt at face value	$ 18,450		$ 16,687
Net unamortized discounts and premiums (1)	(1,606)	[1]	(1,616)	[1]
Total borrowings	16,844		15,071
Capital lease obligation	21		21
Less short-term debt	500		0
Total long-term debt	$ 16,365		$ 15,092

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