The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Intangible Assets (Intangible Assets Subject to Amortization) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Apr. 01, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 474	$ 145	$ 698	$ 475
Gross Carrying Value	8,002		8,002			$ 8,318
Accumulated Amortization	(7,084)		(7,084)			(6,549)
Net Carrying Value	918		918		$ 1,650	1,769
Impairments	19		231	$ 0
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	6,563		6,563			6,563
Accumulated Amortization	(6,321)		(6,321)			(6,029)
Net Carrying Value	242		242			534
Favorable spectrum leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	802		802			763
Accumulated Amortization	(215)		(215)			(150)
Net Carrying Value	587		587			613
Favorable tower leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	0		0			335
Accumulated Amortization	0		0			(215)
Net Carrying Value	0		0			120
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	520		520			520
Accumulated Amortization	(482)		(482)			(89)
Net Carrying Value	38		38			431
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	117		117			137
Accumulated Amortization	(66)		(66)			(66)
Net Carrying Value	51		51			71
Total other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,439		1,439			1,755
Accumulated Amortization	(763)		(763)			(520)
Net Carrying Value	676		$ 676			$ 1,235
Minimum \| Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Useful Lives			5 years
Maximum \| Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Useful Lives			8 years
Maximum \| Favorable spectrum leases
Finite-Lived Intangible Assets [Line Items]
Useful Lives			23 years
Maximum \| Favorable tower leases
Finite-Lived Intangible Assets [Line Items]
Useful Lives			0 years
Maximum \| Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Useful Lives			1 year
Maximum \| Other
Finite-Lived Intangible Assets [Line Items]
Useful Lives			10 years
Intangible Assets, Amortization Period
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 381		$ 381
Impairment effect on earnings per share (in usd per share)	$ 0.07		$ 0.07