Leases (Lease Cost and Additional Information) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 371
Short-term lease cost	8
Variable lease cost	150
Sublease income	(18)
Net lease cost	511
Operating cash outflows from operating leases	392
Right of use assets obtained in exchange for new operating lease liabilities	$ 140
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term – real estate	8 years 9 months 10 days
Weighted-average discount rate – real estate leases	3.10%