Derivatives - Change in the Fair Value for Interest Rate Contracts and Related Hedged Items (Details) - Fair Value Hedging - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Long-Term Debt
Derivatives, Fair Value [Line Items]
Carrying Amount of Hedged Item	$ 4,132		$ 4,132
Cumulative amount of fair value hedging adjustments included in the carrying amount of hedged items	(394)		(394)
Interest Rate Contract \| Interest Expense, Long-Term Debt
Derivatives, Fair Value [Line Items]
Change in fair value of interest rate swaps hedging long-term debt	89	$ (18)	143	$ (81)
Change in fair value of hedged long-term debt	$ (87)	$ 19	$ (140)	$ 83

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Amount of unrealized gain (loss) included in earnings related to the fair value of the hedged item in an interest rate fair value hedge, offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
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-Publisher FASB
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-Section 50
-Paragraph 4C
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-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Amount of unrealized gain (loss) related to the fair value of interest rate derivatives designated as fair value hedging instruments, as offset by the gain (loss) on the hedged item to the extent that the fair value hedge is determined to be effective.

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