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, 2014		$ 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)
Share-based compensation and other, net			40
Dividends declared			(211)		(395)
Other comprehensive income	$ 58			58
Net income	335				335
Balance at end of period at Jun. 30, 2015	14,587	563	15,896	(1,959)	87
Balance at beginning of period at Dec. 31, 2015	14,060	544	15,178	(1,934)	272
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		2	3
Repurchase of common stock		0	0
Shares withheld to satisfy tax withholdings			(14)
Share-based compensation and other, net			38
Dividends declared			0		(589)
Other comprehensive income	53			53
Net income	432				432
Balance at end of period at Jun. 30, 2016	$ 13,985	$ 546	$ 15,205	$ (1,881)	$ 115