Leases - Disclosures related to periods prior to adoption of new lease standard (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Leases
Rental expense under operating leases	$ 393

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

No definition available.

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