Earnings Per Share - Antidilutive Securities Excluded from Computation of EPS Table (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments		$ 3	$ 0	$ 14
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		3	1	3
5.75% Cumulative Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 21	$ 21	$ 64	$ 64
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	59	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	$ 47	$ 47
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	42	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	$ 8	$ 8
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	$ 9	$ 9
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	6	6	6	6