Employee Benefit Plans and Stockholders' Equity - Restricted Stock Units Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares
Nonvested at beginning of period (shares)	2.7
Nonvested at end of period (shares)	1,800,000	2.7
Unvested restricted stock units
Shares
Nonvested at beginning of period (shares)	2,700,000	2,700,000	3,700,000
Granted (shares)	700,000	1,700,000	1,300,000
Vested (shares)	(1,400,000)	(1,400,000)	(1,900,000)
Forfeited (shares)	(200,000)	(300,000)	(400,000)
Nonvested at end of period (shares)	1,800,000	2,700,000	2,700,000
Weighted Average Grant Date Fair Value
Nonvested at beginning of period (USD per share)	$ 69.19	$ 70.68	$ 62.51
Granted (USD per share)	144.37	66.07	75.78
Vested (USD per share)	69.45	68.44	58.92
Forfeited (USD per share)	83.45	68.56	67.97
Nonvested at end of period (USD per share)	$ 96.63	$ 69.19	$ 70.68
Aggregate Intrinsic Value	$ 392.0	$ 319.0	$ 154.5

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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-Publisher FASB
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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