Employee Benefit Plans (Details 4) - Pension Benefits - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 31, 2015	Mar. 31, 2014
Defined Benefit Plans
Fair value of plan assets	$ 2,189,900	$ 2,348,795	$ 2,426,013
Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	210,878	374,802
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	1,268,633	1,275,485
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets	710,389	698,508
Interest-bearing cash
Defined Benefit Plans
Fair value of plan assets	33,271
Interest-bearing cash | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	33,271
U.S. Government securities
Defined Benefit Plans
Fair value of plan assets	68,367
U.S. Government securities | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	62,428
U.S. Government securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	5,939
Corporate Debt Securities
Defined Benefit Plans
Fair value of plan assets	405,993
Corporate Debt Securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	405,898
Corporate Debt Securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets	95	187	199
Common Stock
Defined Benefit Plans
Fair value of plan assets	95,770
Common Stock | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	88,928
Common Stock | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	6,842
Partnership or joint venture interest
Defined Benefit Plans
Fair value of plan assets	709,251
Partnership or joint venture interest | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	0
Partnership or joint venture interest | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets	709,251	746,305	689,073
Other investments
Defined Benefit Plans
Fair value of plan assets	2,096
Other investments | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	156
Other investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	1,940
Common/collective trusts
Defined Benefit Plans
Fair value of plan assets	609,852
Common/collective trusts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	609,852
Registered investment companies
Defined Benefit Plans
Fair value of plan assets	224,062
Registered investment companies | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets	59,366
Registered investment companies | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	164,696
Value of funds in insurance company accounts
Defined Benefit Plans
Fair value of plan assets	41,238
Value of funds in insurance company accounts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets	40,195
Value of funds in insurance company accounts | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets	$ 1,043	1,076	$ 1,131
Continuing Operations
Defined Benefit Plans
Fair value of plan assets		2,513,763
Continuing Operations | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		401,126
Continuing Operations | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		1,365,069
Continuing Operations | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets		747,568
Continuing Operations | Interest-bearing cash
Defined Benefit Plans
Fair value of plan assets		3,279
Continuing Operations | Interest-bearing cash | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		3,279
Continuing Operations | U.S. Government securities
Defined Benefit Plans
Fair value of plan assets		170,484
Continuing Operations | U.S. Government securities | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		158,938
Continuing Operations | U.S. Government securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		11,546
Continuing Operations | Corporate Debt Securities
Defined Benefit Plans
Fair value of plan assets		410,222
Continuing Operations | Corporate Debt Securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		410,035
Continuing Operations | Corporate Debt Securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets		187
Continuing Operations | Common Stock
Defined Benefit Plans
Fair value of plan assets		116,221
Continuing Operations | Common Stock | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		110,932
Continuing Operations | Common Stock | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		5,289
Continuing Operations | Partnership or joint venture interest
Defined Benefit Plans
Fair value of plan assets		746,305
Continuing Operations | Partnership or joint venture interest | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets		746,305
Continuing Operations | Other investments
Defined Benefit Plans
Fair value of plan assets		3,126
Continuing Operations | Other investments | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		5
Continuing Operations | Other investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		3,121
Continuing Operations | Common/collective trusts
Defined Benefit Plans
Fair value of plan assets		743,960
Continuing Operations | Common/collective trusts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		743,960
Continuing Operations | Registered investment companies
Defined Benefit Plans
Fair value of plan assets		276,900
Continuing Operations | Registered investment companies | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		131,251
Continuing Operations | Registered investment companies | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		145,649
Continuing Operations | Value of funds in insurance company accounts
Defined Benefit Plans
Fair value of plan assets		43,266
Continuing Operations | Value of funds in insurance company accounts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		42,190
Continuing Operations | Value of funds in insurance company accounts | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets		1,076
Spinoff
Defined Benefit Plans
Fair value of plan assets		164,968
Spinoff | Quoted Prices in Active Markets for Identical Assets (Level1)
Defined Benefit Plans
Fair value of plan assets		26,324
Spinoff | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans
Fair value of plan assets		89,584
Spinoff | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans
Fair value of plan assets		$ 49,060