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Employee Benefit Plans - Individually Significant Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Multiemployer Plans [Line Items] |  |  |  |
High end of funded percentage of multiemployer plans in critical status |  | 65.00% |  |
High end of funded percentage of multiemployer plans in endangered status |  | 80.00% |  |
Surcharge percentage during first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical |  | 5.00% |  |
Period for which surcharge is 5% on contribution rates for plans certified as endangered, seriously endangered or critical |  | 12 months |  |
Accrued benefit liabilities |  | $ 29 | $ 37 |
Surcharge percentage after first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical |  | 10.00% |  |
Minimum percentage of total contributions provided by the Company relating to multiemployer plans |  | 5.00% |  |
Company Contributions |  | $ 47 | 47 | $ 43
Minimum [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Projected insolvency period |  | 15 years |  |
Maximum [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Projected insolvency period |  | 20 years |  |
Western Pennsylvania Teamsters and Employers Pension Plan [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Company Contributions |  | $ 1 | 1 | 1
Multiemployer Health and Welfare Plan [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Company Contributions |  | 42 | $ 40 | 33
Withdrawal from Multiemployer Pension Plans [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Charge to "Operating" expenses | $ 11 | 12 |  | $ 51
Withdrawal from Multiemployer Pension Plans [Member] | Western Pennsylvania Teamsters and Employers Pension Plan [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Charge to "Operating" expenses |  | $ 11 |  |

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