Lease Commitments - Lease Maturity Prior to Topic 842 (Details) $ in Millions	Dec. 31, 2018 USD ($)
Gross rental commitments
2019	$ 303
2020	253
2021	221
2022	182
2023	148
Thereafter	472
Total minimum payments required	1,579
Rentals from subleases
2019	(34)
2020	(30)
2021	(30)
2022	(30)
2023	(12)
Thereafter	(5)
Total minimum payments required	(141)
Operating Lease Payments Net Of Sublease Rental Income [Abstract]
2019	269
2020	223
2021	191
2022	152
2023	136
Thereafter	467
Total minimum payments required	$ 1,438

Operating Lease, Future Minimum Payments Due, Future Minimum Sublease Rental Payments, After Year Five

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Operating Lease Future Minimum Payments Due Future Minimum Sublease Rentals

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Operating Lease, Future Minimum Payments Due, Future Minimum Sublease Rentals, Year Four

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Operating Lease, Future Minimum Payments Due, Net Of Sublease Income, Next Twelve Months

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Operating Lease Payments Net Of Sublease Rental Income [Abstract]

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Year Five

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Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Year Two

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Operating Leases, Future Minimum Payments Due, Future Sublease Rentals, Year Three

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Operating Leases, Future Minimum Payments Net Of Sublease Rentals, Due After Year Five

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Operating Leases, Future Minimum Payments Net Of Sublease Rentals, Due In Five Years

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Operating Leases, Future Minimum Payments Net Of Sublease Rentals, Due In Four Years

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Operating Leases, Future Minimum Payments Net Of Sublease Rentals, Due In Three Years

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Operating Leases, Future Minimum Payments Net Of Sublease Rentals, Due In Two Years

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Sublease Income, Payments Due [Abstract]

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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