Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Unrealized gains (losses) on cash flow hedging instruments:
Balance at beginning of period		$ (41)	$ (83)	$ (52)	$ (97)
Net gains arising during period, net of tax		7	7	16	19
Reclassification adjustment for losses realized in net income, net of tax	[1]	2	2	4	4
Total other comprehensive income for period		9	9	20	23
Balance at end of period		(32)	(74)	(32)	(74)
Net gains arising during period, tax		4	4	9	9
Reclassification adjustment for losses realized in net income, taxes		1	1	2	2
Pension and postretirement benefit plan liability:
Balance at beginning of period		(13)	(11)	(13)	(11)
Balance at end of period		(13)	(11)	(13)	(11)
Total accumulated other comprehensive loss at end of period		$ (45)	$ (85)	$ (45)	$ (85)	$ (65)

[1] The amounts reclassified during the three and six months ended June 30, 2015 and 2014 relate to interest rate and currency swaps and are included as a component of interest expense in our consolidated statement of income.