Equity Equity (Preferred Stock Dividends) (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended
Mar. 05, 2020	Feb. 18, 2020	Mar. 05, 2019	Feb. 15, 2019	Mar. 31, 2020	Mar. 31, 2019
Preferred Stock
Dividends Payable [Line Items]
Dividends Payable, Date Declared	Mar. 05, 2020	Feb. 18, 2020	Mar. 05, 2019	Feb. 15, 2019
Dividends Payable, Date of Record	Mar. 01, 2020	Feb. 29, 2020	Feb. 28, 2019	Feb. 28, 2019
Dividends Payable, Date to be Paid	Mar. 16, 2020	Mar. 16, 2020	Mar. 15, 2019	Mar. 15, 2019
Series A Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0.253	$ 0	$ 0.250	$ 0	$ 0.253	$ 0.250
Dividends, Preferred Stock, Cash	$ 6	$ 0	$ 6	$ 0	$ 6	$ 6
Series C Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Series D Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 29.375	$ 0	$ 29.375	$ 29.375	$ 29.375
Dividends, Preferred Stock, Cash	$ 0	$ 15	$ 0	$ 15	$ 15	$ 15
Series E Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 351.563	$ 0	$ 351.563	$ 351.563	$ 351.563
Dividends, Preferred Stock, Cash	$ 0	$ 11	$ 0	$ 11	$ 11	$ 11
Series F Preferred Stock [Member]
Dividends Payable [Line Items]
Preferred Stock, Dividends Per Share, Declared	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Dividends, Preferred Stock, Cash	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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