Discontinued Operations - Narrative (Details) $ in Millions		12 Months Ended
	May 01, 2017 USD ($) agreement	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents of discontinued operations		$ 0	$ 5	$ 2	$ 4
Tempo Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of commercial agreements | agreement	2
Tempo Business | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price	$ 4,300
Gain on sale of discontinued operations, net of tax		779	0	0
Depreciation of fixed assets		8	70	65
Intangible asset amortization		11	120	$ 141
Cash and cash equivalents of discontinued operations		0	$ 5
Maximum | Tempo Business | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price	4,200
Deferred consideration	$ 500
Tradenames | Tempo Business | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of intangible assets associated with divested business		$ 380