Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Dividends Payable [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid		$ 17.1875	$ 17.1875	$ 17.1875	$ 17.1875
Common Stock, Dividends, Per Share, Cash Paid	[1]	$ 1.125	$ 1.125	$ 1.125
Dividends, Common Stock, Cash	[1]	$ 472	$ 471	$ 471
Dividends, Preferred Stock, Cash		28	$ 28	$ 28	$ 28
Common stock repurchased during period, shares						0.4
Purchases of Common Stock						$ (44)	$ (34)
Availability Under ATM		$ 750				$ 750
Common Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	[1]	Aug. 08, 2019	May 16, 2019	Feb. 21, 2019
Dividends Payable, Date of Record	[1]	Sep. 13, 2019	Jun. 14, 2019	Mar. 15, 2019
Dividends Payable, Date to be Paid	[1]	Sep. 30, 2019	Jun. 28, 2019	Mar. 29, 2019
Preferred Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared		Sep. 18, 2019	Jun. 17, 2019	Mar. 19, 2019	Dec. 11, 2018
Dividends Payable, Date of Record		Oct. 15, 2019	Jul. 15, 2019	Apr. 15, 2019	Jan. 15, 2019
Dividends Payable, Date to be Paid		Nov. 01, 2019	Aug. 01, 2019	May 01, 2019	Feb. 01, 2019

[1] Inclusive of dividends accrued for holders of unvested restricted stock units, which will be paid when and if the restricted stock units vest.