Intangible Assets (Intangible Assets Subject to Amortization) (Details) (USD $) In Millions, unless otherwise specified															6 Months Ended
Sep. 30, 2014 Successor [Member]	Mar. 31, 2014 Successor [Member]	Sep. 30, 2014 Successor [Member] Customer Relationships [Member]	Mar. 31, 2014 Successor [Member] Customer Relationships [Member]	Sep. 30, 2014 Successor [Member] Favorable spectrum leases [Member]	Mar. 31, 2014 Successor [Member] Favorable spectrum leases [Member]	Sep. 30, 2014 Successor [Member] Favorable tower leases [Member]	Mar. 31, 2014 Successor [Member] Favorable tower leases [Member]	Sep. 30, 2014 Successor [Member] Trademarks [Member]	Mar. 31, 2014 Successor [Member] Trademarks [Member]	Sep. 30, 2014 Successor [Member] Other Finite Lived Intangible Assets [Member]	Mar. 31, 2014 Successor [Member] Other Finite Lived Intangible Assets [Member]	Sep. 30, 2014 Successor [Member] Finite Lived Intangible Assets Excluding Customer Relationships [Member]	Mar. 31, 2014 Successor [Member] Finite Lived Intangible Assets Excluding Customer Relationships [Member]	Sep. 30, 2014 Minimum [Member] Customer Relationships [Member]	Sep. 30, 2014 Minimum [Member] Favorable tower leases [Member]	Sep. 30, 2014 Minimum [Member] Other Finite Lived Intangible Assets [Member]	Sep. 30, 2014 Maximum [Member] Customer Relationships [Member]	Sep. 30, 2014 Maximum [Member] Favorable spectrum leases [Member]	Sep. 30, 2014 Maximum [Member] Favorable tower leases [Member]	Sep. 30, 2014 Maximum [Member] Trademarks [Member]	Sep. 30, 2014 Maximum [Member] Other Finite Lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life															4 years	3 years	4 years	8 years	23 years	7 years	34 years	10 years
Gross Carrying Value	$ 8,983	$ 8,976	$ 6,923	$ 6,923	$ 884	$ 884	$ 589	$ 589	$ 520	$ 520	$ 67	$ 60	$ 2,060	$ 2,053
Accumulated Amortization	(2,287)	(1,418)	(2,071)	(1,289)	(51)	(30)	(134)	(80)	(19)	(12)	(12)	(7)	(216)	(129)
Net Carrying Value	$ 6,696	$ 7,558	$ 4,852	$ 5,634	$ 833	$ 854	$ 455	$ 509	$ 501	$ 508	$ 55	$ 53	$ 1,844	$ 1,924

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration