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Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0
PAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 11.0
Weighted-average remaining requisite service period	13 months
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Unrecognized compensation cost	$ 25.5
Weighted-average remaining requisite service period	19 months
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Unrecognized compensation cost	$ 2.2
Weighted-average remaining requisite service period	22 months
Expiration period	10 years
Elanco Stock Compensation Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock to be reserved for future issuance (in shares)	11,000,000	5,500,000		5,500,000
Stock-based compensation	$ 40.7	$ 1.8
Lilly's Stock-Based Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 5.1	$ 26.0	$ 25.0