Reconciliation of income tax computed at US Federal tax rates (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statutory Income Tax	35.00%	35.00%	35.00%
Prior Year Tax Settlements	(14.50%)	0.50%	0.30%
Foreign Items	(0.60%)	(1.30%)	(0.80%)
Tax Credits	(7.60%)	(0.60%)	0.00%
Other Items, Net	(3.80%)	(0.20%)	(0.50%)
Effective Tax	8.50%	33.40%	34.00%