Employee Pension and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Fair Value of Assets in Pension Plan and Other Benefits Plan

The following table sets forth the fair value of the assets in the Company's Pension Plan and Other Benefits Plan as of December 31, 2017 and 2016.

	Pension Plan						Other Benefits Plan
	Years Ended December 31,						Years Ended December 31,
(Dollars in millions)	2017			2016			2017			2016
Change in plan assets:
Fair value of plan assets, beginning of year	$	3,254		$	2,992		$	260		$	254
Actual return on plan assets	608			221			44			17
Employer contributions	115			150			1			9
Plan participants' contributions	—			—			4			8
Benefits paid	(123		)	(109		)	(21		)	(28		)
Fair value of plan assets, end of year	$	3,854		$	3,254		$	288		$	260

Fair Value by Level Within Fair Value Hierarchy Assets by Major Asset Category for Pension Plan and Other Benefits Plan

	December 31, 2017
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Other Postretirement Benefits Plan Investments:
Cash and cash equivalents	$	—	$	3	$	—	$	3
U.S. government securities	—		44		—		44
Fixed and variable income securities	—		29		—		29
Municipal bonds	—		1		—		1
Mutual funds	66		—		—		66
Total investments in the fair value hierarchy	$	66	$	77	$	—	$	143
Investments measured at net asset value (1)							157
Investments at fair value							300
Net pending trades							(12		)
Total plan assets							$	288

(1) In accordance with ASU No. 2015-07, investments in which fair value was measured based on net asset value per share (or its equivalent) using the practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in these tables are intended to permit reconciliation of the fair value hierarchy to total plan assets.

	December 31, 2016
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Other Postretirement Benefits Plan Investments:
U.S. government securities	$	—	$	40	$	—	$	40
Fixed and variable income securities	—		26		—		26
Mutual funds	128		—		—		128
Total investments in the fair value hierarchy	$	128	$	66	$	—	$	194
Investments measured at net asset value (1)							72
Investments at fair value							266
Net pending trades							(6		)
Total plan assets							$	260

(1) In accordance with ASU No. 2015-07, investments in which fair value was measured based on net asset value per share (or its equivalent) using the practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in these tables are intended to permit reconciliation of the fair value hierarchy to total plan assets.

The following table provides the fair value by level within the fair value hierarchy of the Company's period-end assets by major asset category for the Pension Plan and Other Benefits Plan. For information about the fair value hierarchy levels, refer to Note 11 to these consolidated financial statements. The Plans do not hold any equity or debt securities issued by the Company or any related parties.

	December 31, 2017
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Pension Plan Investments:
Cash and cash equivalents	$	—	$	26	$	—	$	26
U.S. government securities	—		195		—		195
Fixed and variable income securities	—		638		—		638
Equity securities	381		7		—		388
Mutual funds	830		—		—		830
Municipal bonds	—		43		—		43
Other	5		11		—		16
Total investments in the fair value hierarchy	$	1,216	$	920	$	—	$	2,136
Investments measured at net asset value (1)							1,704
Investments at fair value							3,840
Accrued dividends and interest receivable							8
Net pending trades							6
Total plan assets							$	3,854

(1) In accordance with ASU No. 2015-07, investments in which fair value was measured based on net asset value per share (or its equivalent) using the practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in these tables are intended to permit reconciliation of the fair value hierarchy to total plan assets.

	December 31, 2016
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Pension Plan Investments:
Cash and cash equivalents	$	—	$	9	$	—	$	9
U.S. government securities	—		219		—		219
Fixed and variable income securities	—		476		—		476
Equity securities	333		6		—		339
Mutual funds	685		—		—		685
Municipal bonds	—		22		—		22
Other	2		11		—		13
Total investments in the fair value hierarchy	$	1,020	$	743	$	—	$	1,763
Investments measured at net asset value (1)							1,493
Investments at fair value							3,256
Accrued dividends and interest receivable							7
Net pending trades							(9		)
Total plan assets							$	3,254

Defined Benefit Plans Disclosures

The following tables as of December 31, 2017 and 2016 present the Company's Pension Plan and Other Benefits Plan investments in which fair value is measured using net asset value per share (or its equivalent) as a practical expedient.

	December 31, 2017
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Pension Plan Investments
Domestic equity funds	$	1,101	$	—	Daily	None	None
Real estate funds	343		—		Quarterly	Availability of fund's liquid assets and approval of the board of directors	45-90 days
Real estate funds	13		5		None	Hold until dissolution; approximately four to six years from original final closing date	None
International equity funds	228		—		Monthly	None	15 days
Money market funds	19		—		Immediate	None	None
Total	$	1,704	$	5

	December 31, 2016
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Pension Plan Investments
Domestic equity funds	$	936	$	—	Daily	None	None
Real estate funds	329		—		Quarterly	Availability of fund's liquid assets and approval of the board of directors	45-90 days
Real estate funds	20		7		None	Hold until dissolution; approximately five to seven years from original final closing date	None
International equity funds	173		—		Monthly	None	15 days
Money market funds	35		—		Immediate	None	None
Total	$	1,493	$	7

	December 31, 2017
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Other Postretirement Benefits Plan Investments
Domestic equity funds	$	100	$	—	Daily	None	None
Pooled separate account - variable life insurance policies	52		—		Quarterly	Proof of death for death claim redemptions	7 business days
Money market funds	5		—		Immediate	None	None
Total	$	157	$	—

	December 31, 2016
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Other Postretirement Benefits Plan Investments
Domestic equity funds	$	20	$	—	Daily	None	None
Pooled separate account - variable life insurance policies	48		—		Quarterly	Proof of death for death claim redemptions	7 business days
Money market funds	4		—		Immediate	None	None
Total	$	72	$	—

Changes in Fair Value of Assets Measured at Level 3

Table of Benefit Obligation Activity and Funded Status for Each of Plans

The following table sets forth the benefit obligation activity and the funded status for each of the Company's plans at December 31, 2017 and 2016. In addition, the table sets forth the over (under) funded status at December 31, 2017 and 2016. This pension benefits table does not include the obligations for Executive Supplemental Benefit Plans (ESBPs).

	Pension Benefits						Other Postretirement Benefits
	Years Ended December 31,						Years Ended December 31,
(Dollars in millions)	2017			2016			2017			2016
Accumulated benefit obligation	$	3,101		$	2,850
Change in benefit obligation
Benefit obligation, beginning of year	$	2,942		$	2,816		$	261		$	305
Service cost	71			91			6			8
Interest cost	100			103			8			9
Plan participants' contributions	—			—			4			8
Actuarial loss/(gain)	252			117			6			5
Effect of plan amendments	—			(76		)	—			(47		)
Medicare Part D subsidy	—			—			1			1
Benefits paid	(123		)	(109		)	(21		)	(28		)
Benefit obligation, end of year	3,242			2,942			265			261
Fair value of plan assets, end of year	3,854			3,254			288			260
Over (Under) funded status	$	612		$	312		$	23		$	(1	)

Table of Amounts Recognized in Accumulated Other Comprehensive Loss for Pension, Including ESBPs, and Other Benefits

The following table illustrates the changes that were reflected in AOCI during 2017, 2016 and 2015. Pension benefits do not include the ESBPs.

	Pension Benefits						Other Postretirement Benefits
(Dollars in millions)	Net Actuarial (Gain) Loss			Prior Service Credit			Net Actuarial (Gain) Loss			Prior Service Credit
Amounts Recognized in Other Comprehensive Loss:
Balance, December 31, 2014	$	1,044		$	(138	)	$	62		$	(23	)
Arising during the year	89			—			32			—
Recognized in net income during the year	(106		)	17			(12		)	8
Balance, December 31, 2015	$	1,027		$	(121	)	$	82		$	(15	)
Arising during the year	133			(76		)	6			(47		)
Recognized in net income during the year	(75		)	18			(10		)	12
Balance, December 31, 2016	$	1,085		$	(179	)	$	78		$	(50	)
Arising during the year	(101		)	—			(19		)	—
Recognized in net income during the year	(79		)	27			(8		)	21
Balance, December 31, 2017	$	905		$	(152	)	$	51		$	(29	)

At December 31, 2017 and 2016, the following amounts were recognized in accumulated other comprehensive loss for pension, including ESBPs, and other benefits.

	December 31, 2017
	Pension Benefits									Other Postretirement Benefits
(Dollars in millions)	Gross			Tax			Net of Tax			Gross			Tax			Net of Tax
Net actuarial loss	$	905		$	356		$	549		$	51		$	21		$	30
Prior service credit	(152		)	(60		)	(92		)	(29		)	(12		)	(17		)
Pension and other postretirement benefits	753			296			457			22			9			13
Executive Supplemental Benefits Plans
Net actuarial loss	40			16			24			—			—			—
Prior service credit	—			—			—			—			—			—
Executive supplemental benefits plans adjustment	40			16			24			—			—			—
Pension and other postretirement benefits, as adjusted	$	793		$	312		$	481		$	22		$	9		$	13

	December 31, 2016
	Pension Benefits									Other Postretirement Benefits
(Dollars in millions)	Gross			Tax			Net of Tax			Gross			Tax			Net of Tax
Net actuarial loss	$	1,085		$	427		$	658		$	78		$	32		$	46
Prior service credit	(179		)	(70		)	(109		)	(50		)	(20		)	(30		)
Pension and other postretirement benefits	906			357			549			28			12			16
Executive Supplemental Benefits Plans
Net actuarial loss	40			15			25			—			—			—
Prior service credit	—			—			—			—			—			—
Executive supplemental benefits plans adjustment	40			15			25			—			—			—
Pension and other postretirement benefits, as adjusted	$	946		$	372		$	574		$	28		$	12		$	16

Estimated Future Benefit Payments and Subsidies

The following pension and postretirement benefit payments, which reflect expected future service, as appropriate, are expected to be paid over the next 10 years. This table does not include the ESBPs.

(Dollars in millions)	Pension Benefits		Postretirement Benefits
Years ending December 31,
2018	$	147	$	16
2019	157		16
2020	163		17
2021	169		17
2022	175		18
Years 2023 - 2027	977		86

Summary of Weighted Average Assumptions Used in Computing Present Value of Benefit Obligations and Net Periodic Benefit Cost

The following tables summarize the weighted average assumptions used in computing the present value of the benefit obligations and the net periodic benefit cost.

	Pension Benefits				Other Postretirement Benefits
	Years Ended December 31,				Years Ended December 31,
	2017		2016		2017		2016
Discount rate in determining net periodic benefit cost prior to Plan amendments
For service cost	n/a		n/a		n/a		4.23	%
For interest cost	n/a		n/a		n/a		3.43
Discount rate in determining net periodic benefit cost after Plan amendments
For service cost	3.79	%	4.13	%	3.97	%	3.22	%
For interest cost	3.42		3.72		3.19		2.43
Discount rate in determining benefit obligations at year end	3.48		3.98		3.37		3.81
Rate of increase in future compensation levels for determining net periodic benefit cost	4.70		4.70		n/a		n/a
Rate of increase in future compensation levels for determining benefit obligations at year end	4.70		4.70		n/a		n/a
Expected return on plan assets	7.50		7.50		7.50		7.50

Components of Net Periodic Benefit Cost

	Pension Benefits									Other Postretirement Benefits									ESBPs
	Years Ended December 31,									Years Ended December 31,									Years Ended December 31,
(Dollars in millions)	2017			2016			2015			2017			2016			2015			2017		2016			2015
Components of net periodic benefit cost:
Service cost	$	71		$	91		$	96		$	6		$	8		$	10		$	—	$	2		$	1
Interest cost	100			103			110			8			9			12			3		2			2
Expected return on plan assets	(254		)	(235		)	(216		)	(19		)	(19		)	(19		)	—		—			—
Amortization of prior service credit	(27		)	(18		)	(17		)	(21		)	(12		)	(8		)	—		—			—
Recognized net actuarial loss	79			75			106			8			10			12			4		3			3
Curtailment gain	—			—			—			—			—			—			—		(2		)	—
Total net periodic benefit cost	$	(31	)	$	16		$	79		$	(18	)	$	(4	)	$	7		$	7	$	5		$	6

Summary of Amounts Forecasted to be Recognized, Net Periodic Benefit Costs

At December 31, 2017 and 2016, the following amounts were forecasted to be recognized in 2018 and 2017 net periodic benefit cost.

	Years Ended December 31,
	2018						2017
(Dollars in millions)	Pension Benefits			Other Postretirement Benefits			Pension Benefits			Other Postretirement Benefits
Net actuarial loss	$	88		$	5		$	77		$	12
Prior service credit	(27		)	(15		)	(27		)	(21		)
Amounts to be reclassified from AOCI	$	61		$	(10	)	$	50		$	(9	)

Schedule of Assumed Weighted-Average Healthcare Cost Trend Rates

The Company's assumed weighted-average healthcare cost trend rates are as follows.

	Years Ended December 31,
	2017		2016		2015
Healthcare cost trend rate assumed for next year	4.44	%	4.64	%	6.29	%
Rate to which cost trend rate is assumed to decline (the ultimate trend rate)	3.94	%	3.96	%	4.50	%
Year the rate reaches the ultimate trend rate	2026		2026		2026

Schedule of Effect of One-Percentage-Point Change in Assumed Healthcare Cost Trend Rates

The healthcare cost trend rate assumptions have a significant effect on the amounts reported for the Health Plan. A one-percentage-point change in assumed healthcare cost trend rates would have the following effects:

(Dollars in millions)	One-Percentage- Point Increase		One-Percentage- Point Decrease
Effect on total of service and interest cost components in 2018	$	2	$	(2	)
Effect on postretirement benefit obligation at December 31, 2017	33		(28		)