Postretirement Benefit Plans (Employer Contributions to Plans) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Contributions to employee benefit plans
Funded pension plans	$ 28	$ 31	$ 47
Unfunded pension plans	13	13	13
Savings and defined contribution pension plans	18	20	18
Total contributions	$ 59	$ 64	$ 78

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Defined contribution plan employers contribution to funded pension plan.

+ References

No definition available.

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- Definition

Defined contribution plan employers contribution to savings and defined contribution pension plan.

+ References

No definition available.

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- Definition

Defined contribution plan employer's contribution to unfunded pension plan.

+ References

No definition available.

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- Definition

The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

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