Stock Based Awards and Other Equity Instruments - Summary of MSU Activity (Details) - MSUs - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
MSUs outstanding
Unvested outstanding, Beginning balance	389		284		213
Unvested MSUs, Granted	133	[1]	121	[2],[3]	71	[4]
Unvested MSUs, Cancelled	(348)	[5]	(16)
Unvested outstanding, Ending balance	174		389		284
Weighted Average Grant-Date Fair Value Per Share
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Beginning balance	$ 40.99		$ 37.41		$ 30.04
Weighted Average Grant-Date Fair Value Per Share, Granted	28.15	[1]	51.76	[2],[3]	59.40	[4]
Weighted Average Grant-Date Fair Value Per Share, Cancelled	37.94	[5]	58.63
Unvested outstanding, Weighted Average Grant-Date Fair Value Per Share, Ending balance	$ 37.29		$ 40.99		$ 37.41
Aggregate Intrinsic Value
Unvested MSUs outstanding, Aggregate Intrinsic Value	$ 5

[1] MSUs provide for vesting based upon the Company’s total shareholder return, or TSR, performance over the period commencing January 1, 2020 through December 31, 2022 relative to the TSR performance of the Nasdaq Composite Total Return Index. Based upon actual attainment relative to the target performance metric, the grantee has the ability to receive up to 200% of the target number of MSUs originally granted, or to receive none at all.

[2] Inclusive of 42,477 dividend equivalents issued to employees holding non-vested MSU grant awards in conjunction with our special cash dividend declared on November 1, 2019, which will be payable to the holder subject to, and only upon vesting of, the underlying awards.

[3] Inclusive of 78,050 MSUs which provide for vesting based upon the Company’s total shareholder return, or TSR, performance over the period commencing January 1, 2019 through December 31, 2021 relative to the TSR performance of the Nasdaq Composite Total Return Index. Based upon actual attainment relative to the target performance metric, the grantee has the ability to receive up to 200% of the target number of MSUs originally granted, or to be issued none at all.

[4] MSUs provide for vesting based upon the Company’s total shareholder return, or TSR, performance over the period commencing January 1, 2018 through December 31, 2020 relative to the TSR performance of the Nasdaq Composite Total Return Index. Based upon actual attainment relative to the target performance metric, the grantee has the ability to receive up to 200% of the target number of MSUs originally granted, or to be issued none at all.

[5] MSU cancellations primarily reflect performance targets not being attained during the performance period.