Asset Allocations Of Postretirement Benefit Plans (Detail)	12 Months Ended
	Dec. 31, 2012
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	0.00%
Defined benefit plan, target allocation percentage of assets, range maximum	30.00%
Equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	10.00%
Defined benefit plan, target allocation percentage of assets, range maximum	55.00%
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	10.00%
Defined benefit plan, target allocation percentage of assets, range maximum	60.00%
Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	0.00%
Defined benefit plan, target allocation percentage of assets, range maximum	15.00%
Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	0.00%
Defined benefit plan, target allocation percentage of assets, range maximum	10.00%
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	0.00%
Defined benefit plan, target allocation percentage of assets, range maximum	20.00%
Commodities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets, range minimum	0.00%
Defined benefit plan, target allocation percentage of assets, range maximum	25.00%