Reserves for Discounts and Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reserve rollforward
Balance at beginning of period	$ 32.8	$ 21.8
Provision related to current period sales	482.8	327.4
Adjustment related to prior period sales	2.2	(2.7)
Credits/payments made	(459.4)	(313.7)
Balance at end of period	58.4	32.8
Discounts
Reserve rollforward
Balance at beginning of period	6.0	5.8
Provision related to current period sales	178.0	160.9
Adjustment related to prior period sales	(1.3)	(2.0)
Credits/payments made	(176.9)	(158.7)
Balance at end of period	5.8	6.0
Contractual Adjustments
Reserve rollforward
Balance at beginning of period	26.5	16.0
Provision related to current period sales	304.1	165.2
Adjustment related to prior period sales	3.2	(0.7)
Credits/payments made	(282.2)	(154.0)
Balance at end of period	51.6	26.5
Returns
Reserve rollforward
Balance at beginning of period	0.3
Provision related to current period sales	0.7	1.3
Adjustment related to prior period sales	0.3
Credits/payments made	(0.3)	(1.0)
Balance at end of period	$ 1.0	$ 0.3

Bioverativ Inc. 10-K