Change In Projected Benefit Obligation

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- Definition

Defined Benefit Plan Accumulated Other Comprehensive Income Net Prior Service Cost Credit

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- Definition

Defined Benefit Plan Actuarial Gain Loss Recognized in Net Periodic Benefit Cost

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- Definition

Defined benefit plan inactive participants.

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- Definition

Defined Contribution And Defined Benefit Plans [Line Items]

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- Definition

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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- Definition

Description of direction and pattern of change in assumed health care cost trend rate used to measure expected cost of benefits for defined benefit postretirement plan.

+ References

No definition available.

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- Definition

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

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- Definition

Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate.

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- Definition

Amount of net periodic benefit cost (credit) for defined benefit plan.

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- Definition

Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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- Definition

Percentage of investment to total investment within defined benefit plan asset category.

+ References

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

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- Definition

Amount of cost for defined contribution plan.

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- Definition

Amount of increase (decrease) in obligation for pension benefits. Includes, but is not limited to, defined benefit or defined contribution plans. Excludes other postretirement benefits.

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Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions			9 Months Ended		12 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution And Defined Benefit Plans [Line Items]
Defined contribution plan, expense recognized						$ 7.5	$ 7.0	$ 7.1
Inactive participants In defined benefit plan						98.00%
Contribution to defined benefit plan assets						$ 21.1
Benefit obligation, discount rate						0.25%
Decrease in expense for all pension plans						$ (0.2)
Net periodic postretirement benefit cost			$ 1.8	$ 0.9		1.5	3.0	$ 8.9
Scenario, Forecast [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Contribution to defined benefit plan assets					$ 18.5
Nonqualified Defined Benefit Plan [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Contribution to defined benefit plan assets						1.9
Nonqualified Defined Benefit Plan [Member] \| Scenario, Forecast [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Contribution to defined benefit plan assets					1.8
Defined Benefit Pension Plan [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Contribution to defined benefit plan assets						$ 23.0	$ 38.4
Benefit obligation, discount rate						3.25%	3.63%	3.76%
Reduction in projected benefit obligation, mortality assumptions	$ (6.0)	$ (12.0)
Projected benefit obligation of defined benefit plans exceeded the fair value of plan assets						$ 154.4	$ 189.5
Accumulated benefit obligation of defined benefit plans						593.0	605.9
Net periodic postretirement benefit cost			3.6	2.7		3.7	5.0	$ 10.0
Actuarial gain						$ 20.3	4.3
Defined Benefit Pension Plan [Member] \| Long Term Investments [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan assets percentage of asset categories						75.00%
Defined Benefit Pension Plan [Member] \| Liability Hedging [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan assets percentage of asset categories						23.00%
Defined Benefit Pension Plan [Member] \| Short-term Investments [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan assets percentage of asset categories						2.00%
Defined Benefit Pension Plan [Member] \| Fixed Income [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan percentage of target allocation						38.00%
Defined Benefit Pension Plan [Member] \| Domestic Equities [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan percentage of target allocation						27.00%
Defined Benefit Pension Plan [Member] \| International Equities [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan percentage of target allocation						25.00%
Defined Benefit Pension Plan [Member] \| Hedge Funds [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Defined benefit plan percentage of target allocation						10.00%
Defined Benefit Pension Plan [Member] \| Scenario, Forecast [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Net actuarial loss					14.2
Other Postretirement Benefits Plan [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Contribution to defined benefit plan assets						$ 1.2	$ 1.5
Benefit obligation, discount rate						3.01%	3.26%	3.38%
Net periodic postretirement benefit cost			$ (1.8)	$ (1.8)		$ (2.2)	$ (2.0)	$ (1.1)
Actuarial gain						$ (0.7)	$ (1.4)
Assumed health care cost trend rate used in measuring the benefit obligation						The assumed health care cost trend rate represents the rate at which health care costs are assumed to increase. The assumed health care cost trend rate used in measuring the benefit obligation in 2017 is 6.75% for pre-age 65 retirees and 7.25% for post-age 65 retirees. These rates are assumed to decrease gradually to the ultimate health care cost trend rate of 4.5% in 2028 for both groups.
The year the health care cost reaches ultimate trend rate of 4.5%						2028
Increase in the benefit obligation						$ 0.9
Decrease in the benefit obligation						$ 0.8
Other Postretirement Benefits Plan [Member] \| Pre Age 65 [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Assumed health care cost trend rate						6.75%
Other Postretirement Benefits Plan [Member] \| Post Age 65 [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Assumed health care cost trend rate						7.25%
Other Postretirement Benefits Plan [Member] \| Scenario, Forecast [Member]
Defined Contribution And Defined Benefit Plans [Line Items]
Net periodic postretirement benefit cost					2.5
Actuarial gain					2.2
Prior service credit					$ 0.3