Lease Commitments (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rental expenses for operating leases
Rental expense	$ 377	$ 358	$ 413
Sub lease rental income	(57)	(52)	(73)
Net rental expense	320	$ 306	$ 340
Future minimum rental payments under operating leases
Gross rental commitment 2018	318
Gross rental commitment 2019	291
Gross rental commitment 2020	249
Gross rental commitment 2021	226
Gross rental commitment 2022	205
Gross rental commitment thereafter	631
Total gross rental commitments	1,920
Sublease income 2018	(41)
Sublease income 2019	(42)
Sublease income 2020	(35)
Sublease income 2021	(34)
Sublease income 2022	(34)
Sublease income thereafter	(18)
Total future sublease income	(204)
Net rental commitment 2018	277
Net rental commitment 2019	249
Net rental commitment 2020	214
Net rental commitment 2021	192
Net rental commitment 2022	171
Net rental commitment thereafter	613
Total minimum payments required	$ 1,716

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

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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 Four

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

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Operating Leases, Future Minimum Payments Due, Future Sublease Rentals, next twelve months

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For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within one year of the balance sheet date, net of sublease rental income, relating to leases defined as operating.

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Operating Leases, Future Minimum Payments Due, Year Two

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The total of future contractually required payments, net of sublease rental income, on leases defined as operating.

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For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments, net of sublease rental income, due within the fifth year of the balance sheet date relating to leases defined as operating.

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For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments, net of sublease rental income due within the third year of the balance sheet date relating to leases defined as operating.

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For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments, net of sublease rental income, due after the fifth year from the balance sheet date on leases defined as operating.

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For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments, net of sublease rental income, due within the second year of the balance sheet date relating to leases defined as operating.

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Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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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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-Publisher FASB
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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 next 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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Contractually required future rental payments receivable on noncancelable subleasing arrangements.

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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 fourth 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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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 third 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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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 second 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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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after 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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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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The total amount of sublease rental income recognized during the period that reduces the entity's rent expense incurred under operating leases.

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