Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends Payable [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	[1]	$ 1.125	$ 1.125
Dividends declared per share of preferred stock		$ 17.1875	$ 17.1875	$ 17.1875	$ 17.1875	$ 34.3750	$ 34.3750
Dividends, Common Stock, Cash	[1]	$ 471	$ 471
Dividends, Preferred Stock, Cash		28	$ 28	$ 28
Common stock repurchased during period, shares						0.4
Purchases of Common Stock						$ (43)	$ (34)
Availability Under ATM		$ 750				$ 750
Common Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	[1]	May 16, 2019	Feb. 21, 2019
Dividends Payable, Date of Record	[1]	Jun. 14, 2019	Mar. 15, 2019
Dividends Payable, Date to be Paid	[1]	Jun. 28, 2019	Mar. 29, 2019
Preferred Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared		Jun. 17, 2019	Mar. 19, 2019	Dec. 11, 2018
Dividends Payable, Date of Record		Jul. 15, 2019	Apr. 15, 2019	Jan. 15, 2019
Dividends Payable, Date to be Paid		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.