Variable Interest Entities (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		12 Months Ended
		Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015
Assets
Cash and cash equivalents		$ 635	$ 1,054	$ 635	$ 472	$ 985
Accounts receivable			700			705
Other current assets			32			30
Licenses			1,818			1,844
Property, plant and equipment, net			3,679			3,764
Other assets and deferred charges			211			197
Liabilities
Current liabilities			890			944
Variable Interest Entities, Other Disclosures
Total winning bid			338
Investments in unconsolidated entities			423			402
U.S. Cellular
Variable Interest Entities, Other Disclosures
Investments in unconsolidated entities		$ 305	384	305
Consolidated Variable Interest Entities
Assets
Cash and cash equivalents	[1]		2			1
Accounts receivable	[1]		35
Other current assets	[1]		6
Licenses	[1],[2]		649			649
Property, plant and equipment, net	[1]		103			8
Other assets and deferred charges	[1]		9
Total assets	[1]		804			658
Liabilities
Current liabilities	[1]		22
Deferred liabilities and credits	[1]		11			1
Total liabilities	[1]		33			1
Unconsolidated Variable Interest Entities
Variable Interest Entities, Other Disclosures
Investments in unconsolidated entities			5			$ 5
Aggregated Variable Interest Entities
Variable Interest Entities, Other Disclosures
Capital contributions, loans or advances			$ 13	$ 281
Advantage Spectrum L.P. | U.S. Cellular
Variable Interest Entities, Other Disclosures
Federal Communications Commission deposit					$ 60
Licenses won		124		124
Total winning bid		$ 338		$ 338
Designated entity auction discount		25.00%		25.00%
Other auction charges		$ 2		$ 2
King Street Wireless L.P.
Variable Interest Entities, Other Disclosures
Cash distributions paid		60
King Street Wireless, L.P. distribution paid to U.S. Cellular		54
King Street Wireless, L.P. distribution paid to King Street Wireless, Inc.		$ 6

[1] ASU 2015-02 was adopted on a modified retrospective basis and, accordingly, prior year amounts have not been revised to reflect the change in guidance.

[2] Includes payments totaling $338 million made by Advantage Spectrum to the FCC as described above.