Long-term Commitments (Operating Lease Agreements) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Gross Rental Commitments
2017, Gross Rental Commitments	$ 372
2018, Gross Rental Commitments	345
2019, Gross Rental Commitments	297
2020, Gross Rental Commitments	262
2021, Gross Rental Commitments	198
Subsequent years, Gross Rental Commitments	862
Rental from Subleases
2017, Rentals from Subleases	46
2018, Rentals from Subleases	42
2019, Rentals from Subleases	36
2020, Rentals from Subleases	32
2021, Rentals from Subleases	4
Subsequent years, Rentals from Subleases	3
Net Rental Commitments
2017, Net Rental Commitments	326
2018, Net Rental Commitments	303
2019, Net Rental Commitments	261
2020, Net Rental Commitments	230
2021, Net Rental Commitments	194
Subsequent years, Net Rental Commitments	$ 859

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Operating Leases Future Minimum Payments Due, Net of Sublease Receivable [Abstract]

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