Leases - Gross Minimum Rental Commitments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Operating lease commitments
Gross minimum rental commitments (including vacant space below) for 2019	$ 1,581
Gross minimum rental commitments (including vacant space below) for 2020	1,233
Gross minimum rental commitments (including vacant space below) for 2021	914
Gross minimum rental commitments (including vacant space below) for 2022	640
Gross minimum rental commitments (including vacant space below) for 2023	445
Gross minimum rental commitments (including vacant space below) beyond 2023	815
Vacant space for 2019	29
Vacant space for 2020	23
Vacant space for 2021	14
Vacant space for 2022	9
Vacant space for 2023	5
Vacant space beyond 2023	8
Sublease income commitments for 2019	11
Sublease income commitments for 2020	7
Sublease income commitments for 2021	5
Sublease income commitments for 2022	4
Sublease income commitments for 2023	4
Sublease income commitments beyond 2023	2
Capital lease commitments
Capital lease commitments for 2019	3
Capital lease commitments for 2020	3
Capital lease commitments for 2021	3
Capital lease commitments for 2022	3
Capital lease commitments for 2023	2
Capital lease commitments beyond 2023	$ 28

Amount of future rental payments receivable on noncancelable subleasing arrangements due within one year.

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Amount of future rental payments receivable on noncancelable subleasing arrangements due after five years.

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Amount of future rental payments receivable on noncancelable subleasing arrangements due within five years.

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Amount of future rental payments receivable on noncancelable subleasing arrangements due within four years.

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Amount of future rental payments receivable on noncancelable subleasing arrangements due within three years.

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Amount of future rental payments receivable on noncancelable subleasing arrangements due within two years.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within one year of the balance sheet date relating to leases defined as operating.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within the fifth year of the balance sheet date relating to leases defined as operating.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within the fourth year of the balance sheet date relating to leases defined as operating.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within the third year of the balance sheet date relating to leases defined as operating.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within the second year of the balance sheet date relating to leases defined as operating.

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Vacant space, associated with infrastructure reductions and restructuring actions, rental payments within, due after the fifth year from the balance sheet date on leases defined as operating.

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Amount of minimum lease payments for capital leases 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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Amount of minimum lease payments for capital leases 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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Amount of minimum lease payments for capital leases 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 minimum lease payments for capital leases 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 minimum lease payments for capital leases 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 minimum lease payments for capital leases 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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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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