Collaborative and Other Relationships - Ionis (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended						12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets							$ 1,805.2	$ 1,955.4	$ 1,816.3
Research and development							3,990.9	2,280.6	2,597.2
Ionis Pharmaceuticals
Collaborative arrangements and non-collaborative arrangement transactions
License fee					$ 70.0	$ 70.0
Expected license fee and regulatory milestone payments					$ 130.0	130.0
Upfront payment for collaboration agreement			$ 375.0			30.0
Total aducanumab collaboration third party milestone expense	$ 155.0					$ 10.0
Research and development			$ 324.1				11.3	30.0			$ 10.0
Research and development expense asset acquired	$ 45.0
Term of collaboration agreement			10 years		6 years
Total payment to enter collaboration agreement			$ 1,000.0
Investment in common stock, shares purchased (in shares)			11.5
Purchase of common stock			$ 625.0
Prepaid research and discovery services			50.9
Investment in common stock, value			462.9
Premium on purchase of common stock			162.1
Estimated additional payments upon achievement of development and commercial milestones				$ 260.0
Upfront and milestone payments made to collaborative partner				25.0
Expected additional milestone payments when certain sales threshold is met				$ 800.0
Ionis Pharmaceuticals | SOD1
Collaborative arrangements and non-collaborative arrangement transactions
Research and development							28.0	20.0	18.0
Estimated additional payments upon achievement of development and commercial milestones		$ 55.0
Upfront and milestone payments made to collaborative partner		$ 35.0
Ionis Pharmaceuticals | SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Cost of sales, excluding amortization and impairment of acquired intangible assets							$ 286.6	$ 293.0	$ 238.0
Ionis Pharmaceuticals | Minimum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones			125.0
Ionis Pharmaceuticals | Minimum | SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration							11.00%			11.00%
Ionis Pharmaceuticals | Maximum
Collaborative arrangements and non-collaborative arrangement transactions
Estimated additional payments upon achievement of development and commercial milestones			$ 270.0
Ionis Pharmaceuticals | Maximum | SPINRAZA
Collaborative arrangements and non-collaborative arrangement transactions
Percentage of royalties as per collaboration							15.00%			15.00%