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Pension, Savings, And Other Employee Benefits (Narrative) (Details) - USD ($) |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Nov. 20, 2017 | Dec. 31, 2017 | Sep. 30, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Estimated social security benefits age |  |  |  | 65 years |  |
Contributions to qualified plans |  |  |  | $ 5,100,000 | $ 165,000,000 | $ 0
Minimum required outstanding par value to each issue of bonds |  |  |  | $ 300,000,000 | 250,000,000 | 250,000,000
Defined benefit plan, funded status of plan |  |  |  |  | (18,100,000) |
Threshold amortization percentage of projected benefit obligation |  |  |  | 10.00% |  |
Threshold amortization, percentage of market-related value of plan assets |  |  |  | 10.00% |  |
Savings Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Employer investment in qualified defined contribution plan |  |  |  | 100.00% |  |
Maximum percent of employee pre-tax contributions that may be matched by the Company (percent) |  |  |  | 6.00% |  |
Other Benefits |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan, benefit obligation |  | $ 39,562,000 |  | $ 39,562,000 | 35,403,000 | 33,166,000
Fair value of plan assets |  | 18,753,000 |  | 18,753,000 | 16,717,000 | 16,128,000
Employer contributions |  |  |  | 564,000 | 873,000 |
Decrease in interest cost |  |  |  | (1,305,000) | (1,292,000) | (1,413,000)
Defined benefit plan, funded status of plan |  | 20,809,000 |  | 20,809,000 | 18,686,000 |
Defined benefit plan, future amortization of gain (loss) |  | 21,600,000 |  | 21,600,000 |  |
Pension Benefits |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan, benefit obligation |  | 840,884,000 |  | 840,884,000 | 804,542,000 | 816,529,000
Fair value of plan assets |  | 811,244,000 |  | 811,244,000 | 778,872,000 | 638,169,000
Employer contributions |  |  |  | 4,789,000 | 169,230,000 |
Decrease in interest cost |  |  |  | (29,380,000) | (31,216,000) | $ (36,424,000)
Defined benefit plan, funded status of plan |  | 29,640,000 |  | 29,640,000 | $ 25,670,000 |
Defined benefit plan, future amortization of gain (loss) |  | $ 11,800,000 |  | $ 11,800,000 |  |
Postretirement benefit (retirees post January 1, 1993) |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan assumptions used calculating benefit obligation expected long term return on assets |  | 5.95% |  | 5.95% | 6.00% | 6.15%
Qualified pension |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Contributions to qualified plans |  |  | $ 165,000,000 | $ 0 |  |
Defined benefit plan, funded status of plan |  | $ (11,200,000) |  | (11,200,000) |  |
Nonqualified pension |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Defined benefit plan, funded status of plan |  | 40,900,000 |  | 40,900,000 |  |
Nonqualified pension | Pension and Postretirement Plans |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Contributions to qualified plans |  |  |  | 5,400,000 |  |
Expected pension contribution |  | 5,700,000 |  | 5,700,000 |  |
Flexible Benefits Contribution |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Employer contributions |  |  |  | 23,000,000 | $ 21,600,000 | $ 20,800,000
Capital Bank Financial Corporation |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Contributions to qualified plans |  | 5,100,000 |  |  |  |
Defined benefit plan, benefit obligation, business combination | $ 18,500,000 |  |  |  |  |
Defined benefit plan, plan assets, business combination | $ 13,200,000 |  |  |  |  |
Defined benefit plan, benefit obligation |  | 18,700,000 |  | 18,700,000 |  |
Fair value of plan assets |  | $ 18,600,000 |  | $ 18,600,000 |  |
Change in Assumptions for Defined Benefit Plans |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Decrease in interest cost |  |  |  |  | $ 5,800,000 |

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