Leases (Maturities of Lease Liabilities Under Previous Lease Standard) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Capital Leases And Financing Obligations [Abstract]
Total	$ 393
Less than 1 year	4
1 to 3 years	11
3 to 5 years	132
5 years and thereafter	246
Imputed Interest On Capital Leases And Financing Obligations [Abstract]
Total	205
Less than 1 year	20
1 to 3 years	38
3 to 5 years	37
5 years and thereafter	110
Minimum Rental Commitments [Abstract]
Total	581
Less than 1 year	82
1 to 3 years	133
3 to 5 years	111
5 years and thereafter	$ 255