Pension and Other Postretirement Benefits - Schedule of Pension and Postretirement Plans Investment Policy and Weighted Average Asset Allocations (Detail)	Dec. 31, 2012	Dec. 31, 2011
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	55.00%
Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	20.00%
Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	55.00%
Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	25.00%
Other Investments [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	35.00%
Other Investments [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	15.00%
Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	100.00%	100.00%
Plan Assets [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	33.00%	34.00%
Plan Assets [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	50.00%	50.00%
Plan Assets [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	17.00%	16.00%