Employee Benefit Plans - Employee Stock Purchase Plan (Details) shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 period $ / shares shares	Sep. 30, 2019 $ / shares shares	Sep. 30, 2020 period $ / shares shares	Sep. 30, 2019 $ / shares shares
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESPP offering period duration			24 months
ESPP, number of purchase period | period	4		4
ESPP. purchase period			6 months
ESPP, purchase price of common stock, percent			85.00%
Employee stock purchase plan 2008
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares purchased (in shares) | shares	1.3	1.2	2.7	2.4
Average exercise price per share (in dollars per share) | $ / shares	$ 19.68	$ 22.03	$ 19.59	$ 22.04