Equity Incentive Plans - Equity Awards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Incentive Plans [Abstract]
Compensation expense	$ 124	$ 105	$ 125
Income tax benefits	18	17	22
Cash received from exercise of options	111	154	92
Tax benefit realized on options exercised and release of stock restrictions	$ 53	$ 43	$ 28