Earnings Per Share - Antidilutive Securities Excluded from Computation of EPS Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Convertible Debt Securities [Member] | 5.75% Cumulative Convertible Preferred Stock
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	56	56	56	56
Convertible Debt Securities [Member] | 5.75% Cumulative Convertible Preferred Stock Series A
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	39	39	40	39
Convertible Debt Securities [Member] | 5.0% Cumulative Convertible Preferred Stock Series Two Thousand And Five 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	5	5	5	5
Convertible Debt Securities [Member] | 4.50% Cumulative Comvertible 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
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income Adjustments	$ 3	$ 0	$ 14	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2	3	3	4