Retirement Plans (Projected Benefit Obligation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 2,766
Fair value of plan assets at end of year	2,674	$ 2,766
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - current	(29)	(23)
Pension and other postretirement benefits - noncurrent	(1,676)	(1,602)
Pension Benefits [Member]
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year	3,465	2,142
Service cost	97	88	$ 55
Interest cost	127	122	88
Actuarial (gain)/loss	214	137
Benefits paid	(59)	(155)
CTF Acquisition PBO		1,108
Settlements	(486)
Special termination benefits	5	23
PBO at end of year	3,363	3,465	2,142
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	2,766	1,572
Fair value of plan assets acquired		1,120
Actual return on plan assets	378	201
Employer contributions	206	28
Settlements	(486)
Differential payment received from Verizon	(131)
Benefits paid	(59)	(155)
Fair value of plan assets at end of year	2,674	2,766	1,572
Funded status	(689)	(699)
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - noncurrent	(689)	(699)
Accumulated other comprehensive (gain) loss	556	647	584
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Change in projected benefit obligation (PBO) [Roll Forward]
PBO at beginning of year	925	626
Service cost	21	19	19
Interest cost	40	37	30
Plan participants' contributions	7	5
Actuarial (gain)/loss	54	(18)
Benefits paid	(31)	(23)
CTF Acquisition PBO		276
Special termination benefits		3
PBO at end of year	1,016	925	626
Change in plan assets [Roll Forward]
Plan participants' contributions	7	5
Employer contributions	24	18
Benefits paid	(31)	(23)
Funded status	(1,016)	(925)
Amounts recognized in the consolidated balance sheet [Abstract]
Pension and other postretirement benefits - current	(29)	(23)
Pension and other postretirement benefits - noncurrent	(987)	(902)
Accumulated other comprehensive (gain) loss	$ 33	$ (29)	$ (20)