Employee Postretirement Benefits - Schedule of Pension Plan Assets (Detail)			12 Months Ended			12 Months Ended			12 Months Ended
	Dec. 31, 2012 Actual Asset Allocation [Member]	Dec. 31, 2011 Actual Asset Allocation [Member]	Dec. 31, 2012 Target Allocation [Member]	Dec. 31, 2012 Equity securities [Member] Actual Asset Allocation [Member]	Dec. 31, 2011 Equity securities [Member] Actual Asset Allocation [Member]	Dec. 31, 2012 Equity securities [Member] Target Allocation [Member]	Dec. 31, 2012 Fixed income securities [Member] Actual Asset Allocation [Member]	Dec. 31, 2011 Fixed income securities [Member] Actual Asset Allocation [Member]	Dec. 31, 2012 Fixed income securities [Member] Target Allocation [Member]
Asset Category
Target Allocation			100.00%			55.00%			45.00%
Actual Allocation, End of Year	100.00%	100.00%		55.00%	50.00%		45.00%	50.00%