Long-Term Debt (Tables)

6 Months Ended

Sep. 30, 2017

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments [Table Text Block]

	September 30, 2017												March 31, 2017
	Carrying Value		Fair Value Hedge Adjustment			Unamortized Discount (Premium)			Unamortized Debt Issuance Costs		Maturity Amount		Carrying Value
2.7% Senior Notes due July 2019	$	252,310	$	(3,158	)	$	196		$	652	$	250,000	$	252,980
3.95% Senior Notes due July 2024	248,384		—			309			1,307		250,000		248,265
4.75% Senior Notes due March 2026	446,989		—			—			3,011		450,000		446,812
5.625% Senior Notes due January 2044	547,901		—			(3,213		)	5,312		550,000		547,861
6.375% Junior Notes due March 2056	242,156		—			—			7,844		250,000		242,054
5.45% Junior Notes due September 2056	484,099		—			—			15,901		500,000		483,895
Total	$	2,221,839	$	(3,158	)	$	(2,708	)	$	34,027	$	2,250,000	$	2,221,867