Stockholders' Equity - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 29, 2016	Dec. 31, 2010
Class of Stock [Line Items]
Preferred stock, authorized shares	500,000,000	500,000,000
Preferred stock, par value (in usd per share)	$ 0.01	$ 0.01
Preferred stock, outstanding shares	0	0	0
Common shares outstanding plus underlying outstanding stock awards	504,000,000	497,000,000	490,000,000
Stock options outstanding (in shares)	100,000	100,000	200,000
Net unrecognized compensation cost related to unvested stock-based compensation arrangements	$ 6,400,000,000
Compensation cost expected to be expensed in next twelve months, percentage	50.00%
Net unrecognized compensation cost related to unvested stock-based compensation arrangements, weighted average recognition period (in years)	1 year 1 month
Estimated forfeiture rate	28.00%	28.00%	28.00%
Number of shares of common stock granted	100,000	100,000
Common stock available for future issuance to employees (in shares)	116,000,000
Restricted Stock Units
Class of Stock [Line Items]
Fair value of units vested	$ 6,800,000,000	$ 4,300,000,000	$ 2,700,000,000
Minimum
Class of Stock [Line Items]
Award vesting period	2 years
Maximum
Class of Stock [Line Items]
Award vesting period	5 years
February 2016 Program
Class of Stock [Line Items]
Stock repurchase, authorized amount				$ 5,000,000,000
2010 Program
Class of Stock [Line Items]
Stock repurchase, authorized amount					$ 2,000,000,000