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Other Postretirement Benefits - Reconciliation of Fair Value Balances for Net Assets (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended 12 Months Ended
Dec. 31, 2013
Funds for Retiree Health Benefits [Member]
Dec. 31, 2013
Other Postretirement Benefits [Member]
Dec. 31, 2012
Other Postretirement Benefits [Member]
Dec. 31, 2011
Other Postretirement Benefits [Member]
Dec. 31, 2010
Other Postretirement Benefits [Member]
Dec. 31, 2013
Other Postretirement Benefits [Member]
Level 3 [Member]
Dec. 31, 2012
Other Postretirement Benefits [Member]
Level 3 [Member]
Dec. 31, 2013
Other Postretirement Benefits [Member]
Level 3 [Member]
Funds for Retiree Health Benefits [Member]
Dec. 31, 2012
Other Postretirement Benefits [Member]
Level 3 [Member]
Funds for Retiree Health Benefits [Member]
Dec. 31, 2013
Other Postretirement Benefits [Member]
Level 3 [Member]
Investments (including funds for retiree health benefits) [Member]
Dec. 31, 2012
Other Postretirement Benefits [Member]
Level 3 [Member]
Investments (including funds for retiree health benefits) [Member]
Defined Benefit Plan Disclosure [Line Items]                      
Fair value of plan assets at beginning of year $ (31) $ 1,113 $ 1,047 $ 947 $ 942       $ 31 $ 28 $ 31 $ 28
Assets Still Held at Reporting Date - Unrealized Gains/(Losses) (3)               3 2 3 2
Assets Sold During the Year - Realized Gains/(Losses)                            
Purchases Sales and Settlements (8)               8 4 8 4
Transfers (In/Out) of Level 3                    (3)    (3)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR $ (42) $ 1,113 $ 1,047 $ 947 $ 942       $ 42 $ 31 $ 42 $ 31