Borrowings (Long-term Debt Including Unamortized Debt Discounts and Premiums) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Unamortized discount, net	$ (14)	$ (13)
Debt issuance costs	(25)	(10)
Total long-term debt	$ 4,753	2,876
Lease term	20 years
Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes	$ 4,731	2,581
Senior Notes [Member] \| Senior Notes Due March 2018 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	1.50%
Senior Notes	$ 625	625
Senior Notes [Member] \| Senior Notes Due July 2018 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.20%
Senior Notes	$ 275	275
Senior Notes [Member] \| Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	4.45%
Senior Notes	$ 700	700
Senior Notes [Member] \| Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.225%
Senior Notes	$ 256	256
Senior Notes [Member] \| Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.65%
Senior Notes	$ 800	0
Senior Notes [Member] \| Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.00%
Senior Notes	$ 375	375
Senior Notes [Member] \| Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.45%
Senior Notes	$ 350	350
Senior Notes [Member] \| Senior Notes Due 2027 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.20%
Senior Notes	$ 650	0
Senior Notes [Member] \| Senior Notes Due 2028 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.20%
Senior Notes	$ 700	0
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	6.375%
Medium Term Notes	$ 0	250
Finance lease obligation [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	5.45%
Finance lease obligation	$ 61	$ 68

Capital Lease Obligations, Term

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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.

+ References

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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Including the current and noncurrent portions, carrying value at the balance sheet date of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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