CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	COMMON STOCK	ACCUMULATED OTHER COMPREHENSIVE LOSS	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS
Balance at beginning of period at Dec. 31, 2015		$ 544	$ (1,934)	$ 15,178	$ 272
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		2		2
Shares withheld to satisfy tax withholdings				(12)
Share-based compensation and other, net				16
Dividends declared				0	(295)
Other comprehensive income	$ 27		27
Net income	236				236
Balance at end of period at Mar. 31, 2016	14,036	546	(1,907)	15,184	213
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of ASU 2016-09, Improvements to Employee Share-Based Payment Accounting | Restatement adjustment | Accounting Standards Update 2016-09					0
Balance at beginning of period at Dec. 31, 2016	13,399	547	(2,117)	14,970	(1)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		2		2
Shares withheld to satisfy tax withholdings				(14)
Share-based compensation and other, net				15
Dividends declared				(240)	(55)
Other comprehensive income	31		31
Net income	163				163
Balance at end of period at Mar. 31, 2017	$ 13,306	$ 549	$ (2,086)	$ 14,733	110
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of ASU 2016-09, Improvements to Employee Share-Based Payment Accounting | Restatement adjustment | Accounting Standards Update 2016-09					$ 3