Equity Equity (Common Stock Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Dividends Payable [Line Items]
Dividends, Common Stock, Cash							$ 1,263	$ 1,295
Common Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Jul. 06, 2018	Apr. 24, 2018	Jan. 05, 2018	Jul. 07, 2017	Apr. 25, 2017	Jan. 06, 2017
Dividends Payable, Date of Record	Aug. 06, 2018	May 07, 2018	Feb. 05, 2018	Aug. 07, 2017	May 08, 2017	Feb. 06, 2017
Dividends Payable, Date to be Paid	Sep. 13, 2018	Jun. 13, 2018	Mar. 13, 2018	Sep. 13, 2017	Jun. 13, 2017	Mar. 13, 2017
Common Stock, Dividends, Per Share, Cash Paid	$ 0.42	$ 0.42	$ 0.40	$ 0.40	$ 0.40	$ 0.4
Dividends, Common Stock, Cash	$ 419	$ 428	$ 416	$ 427	$ 431	$ 437	$ 1,263		$ 1,295

Aggregate dividends paid during the period for each share of common stock outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Date the declared dividend will be paid, in CCYY-MM-DD format.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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