CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE LOSS	RETAINED EARNINGS
Balance at beginning of period at Dec. 31, 2013		$ 584	$ 17,343	$ (802)	$ 66
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		2	30
Repurchase of common stock		(15)	(441)
Shares withheld to satisfy tax withholdings			(14)
Other comprehensive income	$ 23			23
Net income	396				396
Dividends declared			(289)		(327)
Share-based compensation and other, net			42
Balance at end of period at Jun. 30, 2014	16,598	571	16,671	(779)	135
Balance at beginning of period at Dec. 31, 2014	15,023	569	16,324	(2,017)	147
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		1	7
Repurchase of common stock		(7)	(247)
Shares withheld to satisfy tax withholdings			(17)
Other comprehensive income	58			58
Net income	335				335
Dividends declared			(211)		(395)
Share-based compensation and other, net			40
Balance at end of period at Jun. 30, 2015	$ 14,587	$ 563	$ 15,896	$ (1,959)	$ 87