Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Basic and Dilutive Common Shares Outstanding Used in Determining Net Income Per Share (Detail)

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Summary of Significant Accounting Policies - Basic and Dilutive Common Shares Outstanding Used in Determining Net Income Per Share (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Earnings Per Share [Abstract]      
Basic common shares outstanding 445.0us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 442.6us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 439.2us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Dilutive effect of stock awards 1.4us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment 2.0us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment 1.4us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment
Diluted common shares outstanding 446.4us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 444.6us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 440.6us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Net income per share - basic $ 0.65us-gaap_EarningsPerShareBasic $ 0.22us-gaap_EarningsPerShareBasic $ 0.10us-gaap_EarningsPerShareBasic
Net income per share - diluted $ 0.65us-gaap_EarningsPerShareDiluted $ 0.22us-gaap_EarningsPerShareDiluted $ 0.10us-gaap_EarningsPerShareDiluted