Accumulated Other Comprehensive Income (Loss) Items Reclassified Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

12 Months Ended

Apr. 01, 2017

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Apr. 01, 2017

Mar. 31, 2017

Dec. 31, 2017

Dec. 31, 2018

Dec. 31, 2016

Successor

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

$ (3,052.7)

$ (4,072.6)

Income Tax Benefit (Expense)

161.0

(18.4)

Income (loss) from continuing operations, net of income taxes

$ 233.5

$ 83.9

$ 120.0

$ 208.3

$ 378.0

$ 233.7

$ 101.4

$ 713.1

$ 645.7

Predecessor

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

$ (950.2)

$ (4,070.0)

Income Tax Benefit (Expense)

263.8

94.5

Income (loss) from continuing operations, net of income taxes

$ (319.8)

(195.5)

$ 124.3

(663.8)

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

2.7

11.7

Total before income taxes

(9.1)

(33.4)

Income Tax Benefit (Expense)

3.3

12.4

Income (loss) from continuing operations, net of income taxes

(5.8)

(21.0)

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Health Coverage

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

(5.5)

(20.4)

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Plan

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

(6.3)

(24.7)

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Total before income taxes

2.2

8.9

Income Tax Benefit (Expense)

(0.8)

(3.3)

Income (loss) from continuing operations, net of income taxes

1.4

5.6

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Health Coverage

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

2.3

9.2

Predecessor | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Plan

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

(0.1)

(0.3)

Predecessor | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Total before income taxes

(27.7)

(232.2)

Income Tax Benefit (Expense)

9.1

85.9

Income (loss) from continuing operations, net of income taxes

(18.6)

(146.3)

Predecessor | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Commodity swap contracts | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

(11.0)

(86.1)

Predecessor | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Foreign currency option contracts | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

(16.6)

(145.6)

Predecessor | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Other Contract | Reclassification out of Accumulated Other Comprehensive Income [Member]

Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]

Net periodic benefit costs, excluding service cost/operating expenses

$ (0.1)

$ (0.5)