Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Total assets	$ 161	$ 162
Liabilities:
Total liabilities	3	31
Money Market Funds [Member]
Assets:
Money market funds	83	99
Fixed Income Securities [Member]
Assets:
Investments	37	36
Redeemable Preferred Stock [Member]
Assets:
Investments	40	25
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Total assets	38	38
Liabilities:
Total liabilities	3	31
Significant Other Observable Inputs (Level 2) [Member] | Money Market Funds [Member]
Assets:
Money market funds	0
Significant Other Observable Inputs (Level 2) [Member] | Fixed Income Securities [Member]
Assets:
Investments	37	36
Significant Other Observable Inputs (Level 2) [Member] | Redeemable Preferred Stock [Member]
Assets:
Investments	0
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Total assets	40	25
Liabilities:
Total liabilities	0
Significant Unobservable Inputs (Level 3) [Member] | Money Market Funds [Member]
Assets:
Money market funds	0
Significant Unobservable Inputs (Level 3) [Member] | Fixed Income Securities [Member]
Assets:
Investments	0
Significant Unobservable Inputs (Level 3) [Member] | Redeemable Preferred Stock [Member]
Assets:
Investments	40	25
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Total assets	83	99
Liabilities:
Total liabilities	0	0
Quoted Prices in Active Markets (Level 1) [Member] | Money Market Funds [Member]
Assets:
Money market funds	83	99
Quoted Prices in Active Markets (Level 1) [Member] | Fixed Income Securities [Member]
Assets:
Investments	0
Quoted Prices in Active Markets (Level 1) [Member] | Redeemable Preferred Stock [Member]
Assets:
Investments	0
Foreign Currency Derivatives [Member]
Assets:
Foreign currency derivatives	1	2
Liabilities:
Derivative liabilities	2
Foreign Currency Derivatives [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Foreign currency derivatives	1	2
Liabilities:
Derivative liabilities	2
Foreign Currency Derivatives [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Foreign currency derivatives	0
Liabilities:
Derivative liabilities	0
Foreign Currency Derivatives [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Foreign currency derivatives	0
Liabilities:
Derivative liabilities	0
Electricity commodity derivatives [Member]
Liabilities:
Derivative liabilities	1	3
Electricity commodity derivatives [Member] | Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Derivative liabilities	1	3
Electricity commodity derivatives [Member] | Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Derivative liabilities	0
Electricity commodity derivatives [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Liabilities:
Derivative liabilities	0
Interest rate derivatives [Member]
Liabilities:
Derivative liabilities		28
Interest rate derivatives [Member] | Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Derivative liabilities		28
Interest rate derivatives [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Liabilities:
Derivative liabilities		$ 0