STOCK-BASED COMPENSATION - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					12 Months Ended	1 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 2009 McDermott International, Inc. Long-Term Incentive Plan	May 31, 2009 2009 McDermott International, Inc. Long-Term Incentive Plan	Dec. 31, 2011 2001 Directors and Officers Long-Term Incentive Plan	Oct. 31, 2002 Thrift Plan	Dec. 31, 2011 Thrift Plan	Dec. 31, 2010 Thrift Plan	Dec. 31, 2009 Thrift Plan	Nov. 12, 1991 Thrift Plan	Dec. 31, 2011 The Babcock and Wilcox Company	Dec. 31, 2011 Stock Option	Dec. 31, 2010 Stock Option	Dec. 31, 2009 Stock Option	Dec. 31, 2011 Earnings Per Share, Basic	Dec. 31, 2010 Earnings Per Share, Basic	Dec. 31, 2009 Earnings Per Share, Basic	Dec. 31, 2011 Earnings Per Share, Diluted	Dec. 31, 2010 Earnings Per Share, Diluted	Dec. 31, 2009 Earnings Per Share, Diluted
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Stock based compensation expense impact on earnings per share																$ 0.08	$ 0.07	$ 0.06	$ 0.08	$ 0.07	$ 0.06
Unrecognized estimated compensation expense for nonvested awards, net	$ 16.7
Shares authorized for issuance					9,000,000						15,000,000
Percentage of fair market value that options to purchase are granted, minimum						100.00%
Additional shares authorized for issuance							15,000,000
Matching employer contributions percentage of the first 6% of compensation								50.00%
Options to purchase shares, expiration term				7 years		10 years
Defined contribution plan matching percent of compensation								6.00%
Common stock issued								0	282,022	941,348
Total incremental compensation cost, result of adjustments to stock-based compensation awards												14.5
Total incremental compensation cost, result of adjustments to stock-based compensation awards, recognized												9.3
Common stock dividend yield													0.00%
Total intrinsic value of stock options exercised													8.4	4.0	5.6
Cash received from exercise of stock options													4.8	5.4	1.1
Weighted-average fair value of stock options granted													$ 9.53	$ 25.39	$ 11.57
Fair value of shares vested													3.2	1.6	0
Tax benefits realized related to stock options exercised	0	0.8	1.8
Tax benefits realized related to restricted stock and restricted stock units	$ 0	$ 1.6	$ 3.4