Leases (Summary of Future Minimum Lease Payments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2017	$ 26
2018	19
2019	18
2020	14
2021	14
Remaining years	150
Total	241
Less: income from subleases	0
Net minimum lease payments	241
Less: amount representing interest	53
Capital lease obligations	188	$ 208
Operating Leases, Future Minimum Rental Payments Due, Fiscal Year Maturity [Abstract]
2017	404
2018	362
2019	276
2020	200
2021	85
Remaining years	229
Total	1,556
Less: income from subleases	60
Net minimum lease payments	$ 1,496

Capital Leases Future Minimum Payments Due Net Of Capital Leases Future Minimum Sublease Rentals

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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, net of contractually required future rental payments receivable on noncancelable subleasing arrangements.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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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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Minimum payments receivable in the future under noncancelable subleases.

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