Earnings Per Share - Antidilutive Securities Excluded from Computation of EPS Table (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 0	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1	2
5.75% Cumulative Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 21	$ 21
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	58	59
5.75% Cumulative Convertible Preferred Stock Series A [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 16	$ 16
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	42	42
5.0% Cumulative Convertible Preferred Stock Series 2005 B [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 3	$ 3
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	6
4.50% Cumulative Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 3	$ 3
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	6