Leases - Aggregate Fixed Future Minimum Commitments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Gross Rental Commitments
2019, Gross Rental Commitments	$ 361
2020, Gross Rental Commitments	340
2021, Gross Rental Commitments	277
2022, Gross Rental Commitments	252
2023, Gross Rental Commitments	214
Subsequent years, Gross Rental Commitments	753
Rentals from Subleases
2019, Rentals from Subleases	32
2020, Rentals from Subleases	31
2021, Rentals from Subleases	12
2022, Rentals from Subleases	10
2023, Rentals from Subleases	9
Subsequent years, Rentals from Subleases	32
Net Rental Commitments
2019, Net Rental Commitments	329
2020, Net Rental Commitments	309
2021 Net Rental Commitments	265
2022, Net Rental Commitments	242
2023, Net Rental Commitments	205
Subsequent years, Net Rental Commitments	$ 721

Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals [Abstract]

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

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Operating Leases, Future Minimum Payments, Net of Sublease Receivable, Due In Five Years

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Operating Leases, Future Minimum Payments, Net of Sublease Receivable, Due In Four Years

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Operating Leases Future Minimum Payments, Net of Sublease Receivable, Due In Three Years

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Operating Leases, Future Minimum Payments, Net of Sublease Receivable, Due In Two Years

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Operating Leases, Future Minimum Payments, Net of Sublease Receivable, Due Thereafter

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Amount of lease payments to be received by lessor in fifth fiscal year following latest fiscal year for operating lease. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest statement of financial position date.

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