Segment Information Revenue By Service Offering (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
Revenue from External Customer
Revenue	$ 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
Revenue from External Customer
Revenue									7,757	6,195	5,591
Wholesale Voice Services and Other
Revenue from External Customer
Revenue									$ 472	$ 582	$ 722