Change in Accounting Estimate (Details) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Accounting Changes and Error Corrections [Abstract]
Proceeds and Excess Tax Benefit from Share-based Compensation	$ 2	$ 7
Rapid Rewards Frequent Flier Liability		$ 63
Estimated Impact		20

The aggregate cash inflow comprised of the amount received from (a) employees to acquire the entity's shares under incentive awards, including stock option exercises and restricted stock arrangements, and (b) the excess tax benefit arising from such transactions.

No definition available.

Name:	us-gaap_ProceedsAndExcessTaxBenefitFromSharebasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration