Earnings Per Share - Antidilutive Securities Excluded from Computation of EPS Table (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
5.75% Cumulative Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 21	$ 22	$ 43
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	59	59	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	$ 32
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	42	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	$ 5	$ 5
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	6	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	$ 6	$ 6
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	6	6	6
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 0	$ 3	$ 0	$ 11
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1	3	2	3