Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Dec. 20, 2017	Feb. 09, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 20, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ESPP, minimum holding period	3 months
ESPP, number of shares authorized for issuance (in shares)	2,000,000,000,000
Number of shares available for purchase (in shares)			2,000,000,000,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee contribution percentage into ESPP	10.00%
ESPP discount percentage from market price on last trading day at end of purchase period	5.00%
ESPP offering period	6 months
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options			10 years
Options, outstanding, intrinsic value			$ 39
Options, exercised, intrinsic value			6	$ 11	$ 9
Proceeds from stock options exercised			$ 1	1	1
Stock options | Employee and Officer | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period			3 years
Stock options | Employee and Officer | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period			5 years
Stock options | Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period			1 year
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, vested, fair value			$ 13	$ 30	23
Outstanding (in shares)			1,729,415	1,085,628
Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, vested, fair value			$ 23	$ 96	$ 8
Outstanding (in shares)			1,584,265	1,036,925
Performance-based Restricted Stock Units Subject To Service, Market and Performance Based Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			418,342
Performance-based Restricted Stock Units Subject To Service Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			1,165,923
Restricted Stock Units and Performance-based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost			$ 63
Unrecognized compensation cost, period for recognition			2 years 7 months 24 days
Cash-settled performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			435,327	753,276
Unrecognized compensation cost			$ 4
Liability for settlement			$ 30	$ 18
Weighted average fair value (in usd per share)			$ 79.70	$ 57.04
Cash-settled performance-based restricted stock units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period		2 years
Cash-settled performance-based restricted stock units | Minimum | Cliff Vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period		3 years
Cash-settled performance-based restricted stock units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period		4 years
Cash-settled performance-based restricted stock units | Maximum | Cliff Vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, award vesting period		4 years
2016 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized (in shares)						5,400,000
Shares available for issuance (in shares)			1,800,000