Stock-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended		12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2012 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. 11, 2002 Thrift Plan	Dec. 31, 2010 Thrift Plan	Nov. 12, 1991 Thrift Plan	Dec. 31, 2012 Babcock and Wilcox Company	Dec. 31, 2011 Babcock and Wilcox Company	Dec. 31, 2010 Babcock and Wilcox Company	Dec. 31, 2012 Stock Option	Dec. 31, 2011 Stock Option	Dec. 31, 2010 Stock Option
Stock Based Compensation Activity [Line Items]
Unrecognized estimated compensation expense for nonvested awards, net		$ 24.5
Shares authorized for issuance				9,000,000				15,000,000
Options to purchase shares, maximum expiration term			7 years		10 years
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%
Defined contribution plan matching percent of compensation							6.00%
Common stock issued							282,022
Total incremental compensation cost, result of adjustments to stock-based compensation awards									14.5	5.2	9.3
Common stock dividend yield												0.00%
Total intrinsic value of stock options exercised												1.9	8.4	4.0
Cash received from exercise of stock options												1.4	4.8	5.4
Weighted-average fair value of stock options granted												$ 6.93	$ 9.53	$ 25.39
Fair value of shares vested												3.6	3.2	1.6
Tax benefits realized related to stock options exercised	0.8
Tax benefits realized related to restricted stock and restricted stock units	$ 1.6