Other Commitments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Loss Contingencies [Line Items]
Other commitments - net	$ 617
Letters of credit
Loss Contingencies [Line Items]
Other commitments - net	275
Surety bonds
Loss Contingencies [Line Items]
Other commitments - net	342
Commitments Expiring Less Than One Year
Loss Contingencies [Line Items]
Other commitments - net	7
Commitments Expiring Less Than One Year | Letters of credit
Loss Contingencies [Line Items]
Other commitments - net	7
Commitments Expiring More Than One Year
Loss Contingencies [Line Items]
Other commitments - net	610
Commitments Expiring More Than One Year | Letters of credit
Loss Contingencies [Line Items]
Other commitments - net	268
Commitments Expiring More Than One Year | Surety bonds
Loss Contingencies [Line Items]
Other commitments - net	$ 342