Employee Pension and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018 and 2017.

	Pension Plan						Other Benefits Plan
	Years Ended December 31,						Years Ended December 31,
(Dollars in millions)	2018			2017			2018			2017
Change in plan assets:
Fair value of plan assets, beginning of year	$	3,854		$	3,254		$	288		$	260
Actual return on plan assets	(196		)	608			(18		)	44
Employer contributions	—			115			—			1
Plan participants' contributions	—			—			4			4
Benefits paid	(129		)	(123		)	(19		)	(21		)
Fair value of plan assets, end of year	$	3,529		$	3,854		$	255		$	288

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

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, 2018
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Pension Plan Investments:
Cash and cash equivalents	$	—	$	25	$	—	$	25
U.S. government securities	—		382		—		382
Fixed and variable income securities	—		824		—		824
Equity securities	185		6		—		191
Mutual funds	620		—		—		620
Municipal bonds	—		37		—		37
Other	—		20		—		20
Total investments in the fair value hierarchy	$	805	$	1,294	$	—	$	2,099
Investments measured at net asset value (1)							1,420
Investments at fair value							3,519
Accrued dividends and interest receivable							12
Net pending trades							(2		)
Total plan assets							$	3,529

(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, 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

	December 31, 2018
(Dollars in millions)	Level 1		Level 2		Level 3		Total
Other Postretirement Benefits Plan Investments:
Cash and cash equivalents	$	—	$	1	$	—	$	1
U.S. government securities	—		37		—		37
Fixed and variable income securities	—		32		—		32
Equity securities	—		—		—		—
Mutual funds	54		—		—		54
Total investments in the fair value hierarchy	$	54	$	70	$	—	$	124
Investments measured at net asset value (1)							134
Investments at fair value							258
Net pending trades							(3		)
Total plan assets							$	255

(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, 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
Equity securities	—		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.

Defined Benefit Plans Disclosures

The following tables as of December 31, 2018 and 2017 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, 2018
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Pension Plan Investments
Domestic equity funds	$	789	$	—	Daily	None	None
Real estate funds	415		—		Quarterly	Availability of fund's liquid assets and approval of the board of directors	45-90 days
Real estate funds	7		3		None	Hold until dissolution date	None
International equity funds	159		—		Monthly	None	15 days
Money market funds	50		—		Immediate	None	None
Total	$	1,420	$	3

	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, 2018
(Dollars in millions)	Fair Value		Unfunded Commitment		Redemption Frequency	Other Redemption Restrictions	Redemption Notice Period
Other Postretirement Benefits Plan Investments
Domestic equity funds	$	87	$	—	Daily	None	None
Pooled separate account - variable life insurance policies	46		—		Quarterly	Proof of death for death claim redemptions	7 business days
Money market funds	1		—		Immediate	None	None
Total	$	134	$	—

	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	$	—

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, 2018 and 2017. In addition, the table sets forth the over (under) funded status at December 31, 2018 and 2017. 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)	2018			2017			2018			2017
Accumulated benefit obligation	$	3,038		$	3,101
Change in benefit obligation
Benefit obligation, beginning of year	$	3,242		$	2,942		$	265		$	261
Service cost	80			71			4			6
Interest cost	100			100			8			8
Plan participants' contributions	—			—			4			4
Actuarial loss/(gain)	(246		)	252			(21		)	6
Effect of plan amendments	—			—			—			—
Medicare Part D subsidy	—			—			1			1
Benefits paid	(129		)	(123		)	(19		)	(21		)
Benefit obligation, end of year	3,047			3,242			242			265
Fair value of plan assets, end of year	3,529			3,854			255			288
Over (Under) funded status	$	482		$	612		$	13		$	23

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 2018, 2017 and 2016. 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, 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	)
Arising during the year	218			—			18			—
Recognized in net income during the year	(87		)	26			(5		)	15
Balance, December 31, 2018	$	1,036		$	(126	)	$	64		$	(14	)

At December 31, 2018 and 2017, the following amounts were recognized in accumulated other comprehensive loss for pension, including ESBPs, and other benefits.

	December 31, 2018
	Pension Benefits									Other Postretirement Benefits
(Dollars in millions)	Gross			Tax			Net of Tax			Gross			Tax			Net of Tax
Net actuarial loss	$	1,036		$	273		$	763		$	64		$	18		$	46
Prior service credit	(126		)	(33		)	(93		)	(14		)	(4		)	(10		)
Pension and other postretirement benefits	910			240			670			50			14			36
Executive Supplemental Benefits Plans
Net actuarial loss	32			8			24			—			—			—
Prior service credit	—			—			—			—			—			—
Executive supplemental benefits plans adjustment	32			8			24			—			—			—
Pension and other postretirement benefits, as adjusted	$	942		$	248		$	694		$	50		$	14		$	36

	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		$	238		$	667		$	51		$	14		$	37
Prior service credit	(152		)	(40		)	(112		)	(29		)	(8		)	(21		)
Pension and other postretirement benefits	753			198			555			22			6			16
Executive Supplemental Benefits Plans
Net actuarial loss	40			11			29			—			—			—
Prior service credit	—			—			—			—			—			—
Executive supplemental benefits plans adjustment	40			11			29			—			—			—
Pension and other postretirement benefits, as adjusted	$	793		$	209		$	584		$	22		$	6		$	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,
2019	$	140	$	17
2020	147		17
2021	153		18
2022	160		18
2023	166		18
Years 2024 - 2028	914		82

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,
	2018		2017		2018		2017
Discount rate in determining net periodic benefit cost
For service cost	3.26	%	3.79	%	3.49	%	3.97	%
For interest cost	3.16		3.42		3.02		3.19
Discount rate in determining benefit obligations at year end	4.12		3.48		4.01		3.37
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	5.10		4.70		n/a		n/a
Expected return on plan assets	7.50		7.50		7.50		7.50
Cash balance crediting rate for determining net periodic benefit cost	2.74		3.06		n/a		n/a
Cash balance crediting rate for determining benefit obligations at year end	3.02		2.74		n/a		n/a

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)	2018			2017			2016			2018			2017			2016			2018		2017		2016
Components of net periodic benefit cost:
Service cost	$	80		$	71		$	91		$	4		$	6		$	8		$	—	$	—	$	2
Interest cost	100			100			103			8			8			9			3		3		2
Expected return on plan assets	(268		)	(254		)	(235		)	(21		)	(19		)	(19		)	—		—		—
Amortization of prior service credit	(26		)	(27		)	(18		)	(15		)	(21		)	(12		)	—		—		—
Recognized net actuarial loss	87			79			75			5			8			10			3		4		3
Curtailment gain	—			—			—			—			—			—			—		—		(2		)
Total net periodic benefit cost	$	(27	)	$	(31	)	$	16		$	(19	)	$	(18	)	$	(4	)	$	6	$	7	$	5

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

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,
	2018		2017		2016
Healthcare cost trend rate assumed for next year	4.44	%	4.44	%	4.64	%
Rate to which cost trend rate is assumed to decline (the ultimate trend rate)	3.94	%	3.94	%	3.96	%
Year the rate reaches the ultimate trend rate	2027		2026		2026

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