Earnings Per Share - Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Income from continuing operations	$ 55.0	$ 57.0
Preferred Stock Dividends Income Statement Impact Included in Diluted Earnings Per Share From Continuing Operations	12.0	12.0
Deemed dividend on modification of Series A Convertible Preferred Stock	0.0	(4.0)
Deemed dividend on preferred stock redemption	0.0	(58.0)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Diluted	43.0	(17.0)
Loss from discontinued operations, net of tax	(35.0)	0.0
Net loss attributable to NCR common stockholders	$ 8.0	$ (17.0)
Weighted Average Number of Shares Outstanding, Basic	119.2	122.8
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	4.6	0.0
Diluted (in shares)	123.8	122.8
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.35	$ (0.14)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.29)	0.00
Earnings Per Share, Diluted	$ 0.06	$ (0.14)
Series A Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	27.7	28.8
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1.4	5.4