Pension and Other Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Employee benefits expense	$ 30	$ 27	$ 27
Defined Contribution Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Employer contributions to defined contribution plan	7	7	7
TMS [Member] | Defined Benefit Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Vesting Period	5 years
Total Number of Last Employment Months	120
Employee benefits expense	8	7	9
Highest average compensation consecutive number of months	60
Maximum employee credited service years	25
TMS [Member] | Defined Contribution Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Vesting Period	four years
Annual Maximum Contribution Percentage by Employee	30.00%
Employer Matching Contribution Percentage	66.67%
Maximum Annual Employer Contribution Percentage Per Employee	6.00%
Employer Matching Contribution, Annual Vesting Percentage	25.00%
TMS [Member] | Other Post-employment Benefits [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Vesting Period	10 years
Employee Minimum Age Eligibility For Post Employment Benefits	55
Employee benefits expense	$ 15	$ 13	$ 11