Financial Instruments (Tables)

12 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Carrying Amounts and Estimated Fair Values of Current and Long-Term Debt

The following table presents carrying amounts and estimated fair values of current and long-term debt and financing obligations:

	Carrying amount at March 31, 2018		Estimated Fair Value Using Input Type
			Quoted prices in active markets		Observable		Unobservable		Total estimated fair value
	(in millions)
Current and long-term debt and financing obligations	$	40,820	$	37,549	$	—	$	3,737	$	41,286

	Carrying amount at March 31, 2017		Estimated Fair Value Using Input Type
			Quoted prices in active markets		Observable		Unobservable		Total estimated fair value
	(in millions)
Current and long-term debt and financing obligations	$	40,581	$	33,196	$	4,352	$	5,468	$	43,016