Impairments - Fair-Value Measurements Table (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets held for use	$ 22		$ 37
Fair Value, Inputs, Level 3 [Member] | Income Approach Valuation Technique [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets held for use	$ 22	[1]	$ 37	[1]

[1] The income approach was used to measure fair value.