Segment Information Revenue From External Customers (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment information
Revenue from external customers	$ 2,053	$ 2,062	$ 2,061	$ 2,053	$ 1,914	$ 1,629	$ 1,625	$ 1,609	$ 8,229	$ 6,777	$ 6,313
Core Network Service [Member]
Segment information
Revenue from external customers									7,757	6,195	5,591
Core Network Service [Member] | North America
Segment information
Revenue from external customers									6,208	4,525	3,949
Core Network Service [Member] | Europe
Segment information
Revenue from external customers									835	891	888
Core Network Service [Member] | Latin America
Segment information
Revenue from external customers									714	779	754
Wholesale Voice Services and Other [Member]
Segment information
Revenue from external customers									472	582	722
Wholesale Voice Services and Other [Member] | North America
Segment information
Revenue from external customers									446	530	681
Wholesale Voice Services and Other [Member] | Europe
Segment information
Revenue from external customers									14	19	31
Wholesale Voice Services and Other [Member] | Latin America
Segment information
Revenue from external customers									$ 12	$ 33	$ 10