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Share-Based Payments - Summary of Share-based Compensation Expense Associated with Each Share-based Compensating Programs (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | $ (204.5) | $ (191.2) | $ (168.7)
Subtotal | 211.3 | 225.4 | 181.6
Capitalized share-based compensation costs | (6.2) | (8.9) | (11.5)
Share-based compensation expense included in total cost and expenses | 205.1 | 216.5 | 170.1
Market stock units |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | 40.5 | 30.4 | 27.2
Time-vested restricted stock units |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | 142.6 | 134.0 | 126.6
Cash settled performance units |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | (1.7) | 0.7 | 7.8
Performance units |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | (0.1) | 1.6 | 3.1
Performance stock units settled in stock |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | 7.9 | 15.5 | 4.7
Performance stock units settled in cash |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | 8.6 | 5.5 | 1.7
Employee stock purchase plan |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Share-based compensation expense | 13.5 | 11.5 | 10.5
Nightstar | Share-based Payment Arrangement, Option |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
NST stock options | $ 0.0 | $ 26.2 | $ 0.0

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