Postretirement Benefit Plans (Actuarial Assumptions and Sensitivity Analysis) (Details)	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Weighted average assumptions used to determine net periodic benefit cost, Expected return on plan assets	5.60%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average assumptions used to determine benefit obligations, Discount rate	3.10%	4.00%	3.90%
Weighted average assumptions used to determine benefit obligations, Average compensation growth	3.10%	3.10%	3.10%
Weighted average assumptions used to determine net periodic benefit cost, Discount rate	4.00%	3.90%	4.40%
Weighted average assumptions used to determine net periodic benefit cost, Average compensation growth	3.10%	3.10%	3.40%
Weighted average assumptions used to determine net periodic benefit cost, Expected return on plan assets	6.10%	6.30%	6.40%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average assumptions used to determine benefit obligations, Discount rate	3.60%	4.10%	3.80%
Weighted average assumptions used to determine benefit obligations, Average compensation growth	3.50%	3.50%	3.50%
Weighted average assumptions used to determine net periodic benefit cost, Discount rate	4.10%	3.80%	4.20%
Weighted average assumptions used to determine net periodic benefit cost, Average compensation growth	3.50%	3.50%	3.90%
Weighted average assumptions used to determine net periodic benefit cost, Expected return on plan assets	0.00%	0.00%	0.00%