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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Goodwill and Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended	81 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2011	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Gross carrying value of goodwill	$ 2,260,000,000		$ 2,260,000,000			$ 2,260,000,000
Accumulated impairment of goodwill	2,080,000,000		2,080,000,000			2,080,000,000
Goodwill impairment charge					$ 2,080,000,000	$ 0
Amortization expense on intangible assets	$ 5,150,000	$ 5,232,000	$ 15,306,000	$ 15,542,000
Trademarks
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period			5 years
Trademarks \| Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life			2 years
Trademarks \| Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life			8 years