Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Net unrealized gains (losses) on equity securities in other income (expense)	$ 118.3	$ (41.9)
Net unrealized gains on equity securities in other comprehensive income (loss)			$ 14.7
Securities without readily determinable fair value	$ 55.6	$ 45.5