Supplemental Cash Flow Information - Supplemental Cash Flow Reconciliation (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		36 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Supplemental Cash Flow Information [Abstract]
Interest expense	$ 238	$ 592
Adjustments to reconcile to cash paid for interest:
Net change in accrued interest	(30)	(116)
Capitalized interest	3	0
Amortization of debt issuance costs	(1)	(9)
Net amortization of discounts and premiums	(21)	(81)
Payments for (Proceeds from) Hedge, Financing Activities	0	35
Other Noncash Expense	(1)	(1)
Cash paid for interest	$ 188	$ 420	$ 5,700