Basis of Presentation and Summary of Significant Accounting Policies (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
Change in accounting estimates
Depreciation expense									$ 986	$ 1,048	$ 1,099
Net income	$ 321	$ 268	$ 238	$ 247	$ 216	$ 245	$ 256	$ 253	1,074	$ 970	$ 964
Switch, circuit and cable network equipment | Service life
Change in accounting estimates
Depreciation expense									20
Net income									(12)
Pension, Supplemental and Other Postretirement Benefit Plans | Change in accounting method accounted for as change in estimate
Change in accounting estimates
Decrease in defined benefit plans net periodic benefit cost									$ (7)
Decrease in defined benefit plans net periodic benefit cost (financial effect)									The change in methodology resulted in a decrease of $7 million to our net periodic benefit cost for the year ended December 31, 2015