Capital Structure - Common Stock (Details) - USD ($)				3 Months Ended	12 Months Ended			33 Months Ended
	Feb. 15, 2019	Feb. 01, 2019	Jan. 23, 2019	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Feb. 28, 2019
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Dividends paid per share (in usd per share)				$ 0.145				$ 0.030
Common stock dividends, proposed annual percentage decrease							79.00%
Dividends per common share (in usd per share)					$ 0.12	$ 0.12	$ 0.24
Eligible compensation withholding, up to (as a percent)					10.00%
Exercise price as a percentage of fair value (as a percent)					85.00%
Treasury stock reserved for issuance under the ESPP (in shares)					2,931,188			2,931,188
Capital Allocation Plan
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Stock repurchase program, authorized amount					$ 1,500,000,000.0			$ 1,500,000,000.0
Subsequent Event
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Dividends payable, date declared			Jan. 23, 2019
Dividends per common share (in usd per share)			$ 0.00030
Dividends payable, date to be paid	Feb. 15, 2019
Dividends payable, date of record		Feb. 01, 2019
Subsequent Event | Capital Allocation Plan
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Stock repurchase program, authorized amount									$ 1,000,000,000
Scenario, Plan
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Common stock, dividends, proposed annual amount, per share				$ 0.58			$ 0.0012
Scenario, Plan | Subsequent Event
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Common stock, dividends, proposed annual amount, per share			$ 0.0012
Long-term incentive plans
Common Stock, Employee Stock Purchase Plan and Share Repurchases
Long-term incentive plans (in shares)					17,631,031			17,631,031