Employee Benefits (Details) - USD ($) $ in Millions						12 Months Ended
		Jan. 01, 2018	Jan. 02, 2017	Jan. 02, 2016	Jan. 02, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Nov. 01, 2017	Dec. 31, 2016	Jan. 01, 2015
Employee Benefits
Benefit obligation		$ 16,497	$ 16,714	$ 16,916		$ 16,497	$ 16,714	$ 16,916	$ 16,916	$ 16,497		$ 16,714
Defined Benefit Plan, assumed health care cost trend rates
Health care cost trend rate per year description							range from 5.0% to 6.5% in 2018, 5.0% to 7.0% in 2019, 5.0% to 6.5% in 2020
Ultimate health care cost trend rate (as a percent)			4.50%	4.50%						4.50%		4.50%	4.50%
Effect of change of 100 basis points in the assumed initial health care cost trend rate
Effect on the aggregate of the service and interest cost components of net periodic post-retirement benefit expense (consolidated statements of operations) - Increase							$ 2
Effect on the aggregate of the service and interest cost components of net periodic post-retirement benefit expense (consolidated statements of operations) - Decrease							(2)
Effect on benefit obligation (consolidated balance sheet) - Increase							60
Effect on benefit obligation (consolidated balance sheet) - Decrease							$ (57)
Actuarial assumptions at beginning of year:
Rate of compensation increase (as a percent)			3.25%	3.25%	3.25%
Ultimate health care cost trend rate (as a percent)			4.50%	4.50%						4.50%		4.50%	4.50%
Year that health care cost rate reaches ultimate trend rate			2025	2025	2025		2025	2025
Components of net periodic benefit (income) expense
Expected return on plan assets							$ (668)	$ (739)
Special termination benefit enhancements							$ 16
Actuarial assumptions at end of year:
Rate of compensation increase (as a percent)										3.25%		3.25%
Ultimate health care cost trend rate (as a percent)			4.50%	4.50%						4.50%		4.50%	4.50%
Year that health care cost rate reaches ultimate trend rate			2025	2025	2025		2025	2025
Remaining estimated life of pension plan participants,							approximately 9 to 10 years as of December 31, 2017
Change in benefit obligation
Benefit obligation at beginning of year		(16,497)	$ (16,714)	$ (16,916)		(16,497)	$ (16,714)	$ (16,916)
Benefit obligation at end of year							(16,497)	(16,714)	(16,916)
Change in plan assets
Return on plan assets							$ 1,307	759
Minimum
Actuarial assumptions at beginning of year:
Initial health care cost trend rate			7.00%	5.00%									6.00%
Actuarial assumptions at end of year:
Initial health care cost trend rate										7.00%		5.00%
Maximum
Actuarial assumptions at beginning of year:
Initial health care cost trend rate			5.00%	5.25%									6.50%
Actuarial assumptions at end of year:
Initial health care cost trend rate										5.00%		5.50%
Pension plans
Employee Benefits
Amortization period of the plan shortfall							7 years
Unfunded status										$ 2,062		$ 2,409
Benefit obligation		13,122	$ 13,301	$ 13,349	$ 15,042	13,122	$ 13,301	13,349	15,042	13,122		13,301
Fair value of plan assets		11,060	$ 10,892	$ 11,072	$ 12,571	11,060	10,892	11,072	12,571	11,060		$ 10,892
Employer contributions							100	100	100
Benefits paid by company							5	7	6
Estimated future benefit payments:
2018										1,031
2019										973
2020										951
2021										929
2022										908
2023 - 2026										$ 4,170
Actuarial assumptions at beginning of year:
Expected long-term rate of return on plan assets (as a percent)			6.50%	7.00%	7.50%
Components of net periodic benefit (income) expense
Service cost							63	64	83
Interest cost							411	427	568
Expected return on plan assets							(666)	(732)	(898)
Recognition of prior service (credit) cost							(8)	(8)	5
Recognition of actuarial loss							205	175	161
Net periodic pension benefit expense (income)							5	(61)	(81)
Special termination benefit enhancements							0	13	0
Change in benefit obligation
Benefit obligation at beginning of year		(13,122)	$ (13,301)	$ (13,349)	$ (15,042)	(13,122)	(13,301)	(13,349)	(15,042)
Service cost							63	64	83
Interest cost							411	427	568
Plan amendments							0	2	(100)
Special termination benefits charge							0	13	0
Actuarial loss (gain)							590	487	(800)
Benefits paid by company							(5)	(7)	(6)
Benefits paid from plan assets							1,238	1,034	1,438
Benefit obligation at end of year							(13,122)	(13,301)	(13,349)
Change in plan assets
Fair value of plan assets at beginning of year		11,060	$ 10,892	$ 11,072	$ 12,571	11,060	10,892	11,072	12,571
Return on plan assets							1,306	754	(161)
Employer contributions							100	100	100
Benefits paid from plan assets	[1]						1,238	1,034	1,438
Fair value of plan assets at end of year							11,060	10,892	11,072
Target allocation of plan assets
Expected long-term rate of return on plan assets (as a percent)			6.50%	7.00%	7.50%
Pension plans | Minimum
Actuarial assumptions at beginning of year:
Discount rate (as a percent)			3.50%	3.50%	3.50%
Actuarial assumptions at end of year:
Discount rate (as a percent)										3.44%		3.50%
Pension plans | Maximum
Actuarial assumptions at beginning of year:
Discount rate (as a percent)			4.10%	4.50%	4.10%
Actuarial assumptions at end of year:
Discount rate (as a percent)										3.70%		4.10%
Post-Retirement benefit plans
Employee Benefits
Unfunded status										$ 3,352		$ 3,360
Benefit obligation		3,375	$ 3,413	$ 3,567	$ 3,830	3,375	3,413	3,567	3,830	3,375		3,413
Fair value of plan assets		23	$ 53	$ 193	$ 353	23	53	193	353	23		$ 53
Employer contributions							0	0
Benefits paid by company							298	191	181
Benefits paid, net of participant contributions and direct subsidy receipts							237
Estimated future benefit payments:
2018										293
2019										280
2020										271
2021										262
2022										253
2023 - 2026										1,122
Medicare Part D Subsidy Receipts
2018										(7)
2019										(7)
2020										(7)
2021										(7)
2022										(7)
2023 - 2026										$ (31)
Actuarial assumptions at beginning of year:
Discount rate (as a percent)			3.90%	4.15%	3.80%
Expected long-term rate of return on plan assets (as a percent)			5.00%	7.00%
Components of net periodic benefit (income) expense
Service cost							18	19	24
Interest cost							100	111	140
Expected return on plan assets							(2)	(7)	(21)
Recognition of prior service (credit) cost							20	20	19
Net periodic pension benefit expense (income)							136	146	162
Special termination benefit enhancements							0	3	0
Actuarial assumptions at end of year:
Discount rate (as a percent)										3.53%		3.90%
Change in benefit obligation
Benefit obligation at beginning of year		(3,375)	$ (3,413)	$ (3,567)	$ (3,830)	(3,375)	(3,413)	(3,567)	(3,830)
Service cost							18	19	24
Interest cost							100	111	140
Participant contributions							54	57	57
Direct subsidy receipts							7	5	8
Special termination benefits charge							0	3	0
Actuarial loss (gain)							112	(13)	(148)
Benefits paid by company							(298)	(191)	(181)
Benefits paid from plan assets							31	145	163
Benefit obligation at end of year							(3,375)	(3,413)	(3,567)
Change in plan assets
Fair value of plan assets at beginning of year		$ 23	$ 53	$ 193	$ 353	23	53	193	353
Return on plan assets							1	5	3
Employer contributions							0	0
Benefits paid from plan assets							31	145	163
Fair value of plan assets at end of year							23	53	193
Target allocation of plan assets
Expected long-term rate of return on plan assets (as a percent)			5.00%	7.00%
Post-Retirement benefit plans | Minimum
Actuarial assumptions at beginning of year:
Expected long-term rate of return on plan assets (as a percent)					7.50%
Target allocation of plan assets
Expected long-term rate of return on plan assets (as a percent)					7.50%
Scenario, Forecast | Post-Retirement benefit plans
Employee Benefits
Benefits paid, net of participant contributions and direct subsidy receipts						283
Actuarial assumptions at beginning of year:
Expected long-term rate of return on plan assets (as a percent)		4.00%
Target allocation of plan assets
Expected long-term rate of return on plan assets (as a percent)		4.00%
Change in accounting method accounted for as a change in estimate
Employee Benefits
Combined decrease in pension and post-retirement cost							(122)	(149)
Change from adoption of revised mortality tables
Employee Benefits
Benefit obligation		$ 113	$ (268)	$ (379)		113	(268)	(379)	(379)	$ 113		$ (268)
Change in benefit obligation
Benefit obligation at beginning of year		$ (113)	$ 268	$ 379		(113)	268	379
Benefit obligation at end of year							(113)	268	$ 379
Qualified plan | Pension plans
Employee Benefits
Unfunded status										2,004		$ 2,352
Employer contributions							100	100
Expected employer contribution in 2018										$ 100
Change in plan assets
Employer contributions							100	100
Qualified plan | Pension plans | Interest rate sensitive investments
Target allocation of plan assets
Target asset allocation percentage (as a percent)										45.00%
Qualified plan | Pension plans | Investment grade bonds
Target allocation of plan assets
Target asset allocation percentage (as a percent)										30.00%
Qualified plan | Pension plans | High yield and emerging market bonds
Target allocation of plan assets
Target asset allocation percentage (as a percent)										10.00%
Qualified plan | Pension plans | Diversified strategies
Target allocation of plan assets
Target asset allocation percentage (as a percent)										5.00%
Qualified plan | Pension plans | Interest rate investments with higher returns
Target allocation of plan assets
Target asset allocation percentage (as a percent)										55.00%
Qualified plan | Pension plans | U.S. stocks
Target allocation of plan assets
Target asset allocation percentage (as a percent)										15.00%
Qualified plan | Pension plans | Developed market Non-U.S. stocks
Target allocation of plan assets
Target asset allocation percentage (as a percent)										15.00%
Qualified plan | Pension plans | Diversified multi-asset classes
Target allocation of plan assets
Target asset allocation percentage (as a percent)										7.00%
Qualified plan | Pension plans | Other
Target allocation of plan assets
Target asset allocation percentage (as a percent)										10.00%
Qualified plan | Pension plans | Real estate
Target allocation of plan assets
Target asset allocation percentage (as a percent)										8.00%
Qualified plan | Scenario, Forecast | Pension plans
Actuarial assumptions at beginning of year:
Expected long-term rate of return on plan assets (as a percent)		7.00%
Target allocation of plan assets
Expected long-term rate of return on plan assets (as a percent)		7.00%
Expected long-term return on assets, net of administrative expenses		6.50%
Nonqualified plan | Pension plans
Employee Benefits
Benefits paid by company							7	5
Estimated future benefit payments:
2018										$ 5
Change in benefit obligation
Benefits paid by company							(7)	$ (5)
Level 3 Parent, LLC | Post-Retirement benefit plans
Employee Benefits
Unfunded status											$ (1)
Level 3 Parent, LLC | Qualified plan | Pension plans
Employee Benefits
Unfunded status										20	20
Benefit obligation		$ 167				167	167			167	167
Fair value of plan assets		147				147	147			$ 147	$ 147
Components of net periodic benefit (income) expense
Net periodic pension benefit expense (income)							1
Change in benefit obligation
Benefit obligation at beginning of year		(167)				(167)
Benefit obligation at end of year							(167)
Change in plan assets
Fair value of plan assets at beginning of year		$ 147				$ 147
Fair value of plan assets at end of year							$ 147
CenturyLink, Inc. | Equity and debt securities
Target allocation of plan assets
Target asset allocation percentage (as a percent)										10.00%

[1] Non-U.S. stocks represent investments in stocks of companies based in developed countries outside the U.S. as well as commingled funds. The valuation inputs for non-U.S. stocks are based on the last published price reported on the major stock market on which the securities are traded and are primarily classified as Level 1. The commingled funds are valued at NAV based on the market value of the underlying investments using the same valuation inputs previously described.