CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE LOSS	RETAINED EARNINGS
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of ASU | Accounting Standards Update 2018-02				$ 0	$ 0
Cumulative effect of adoption of ASU | Accounting Standards Update 2014-09					0
Cumulative effect of adoption of ASU | Accounting Standards Update 2016-09					3
Balance at beginning of period at Dec. 31, 2016		$ 547	$ 14,970	(2,117)	(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	14,733	(2,086)	110
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of ASU	(407)
Cumulative effect of adoption of ASU | Accounting Standards Update 2018-02				(407)	407
Cumulative effect of adoption of ASU | Accounting Standards Update 2014-09					297
Cumulative effect of adoption of ASU | Accounting Standards Update 2016-09					0
Balance at beginning of period at Dec. 31, 2017	23,491	1,069	23,314	(1,995)	1,103
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through dividend reinvestment, incentive and benefit plans		10	(6)
Shares withheld to satisfy tax withholdings			(25)
Share-based compensation and other, net			33
Dividends declared			0		(586)
Other comprehensive income	114			114
Net income	115				115
Balance at end of period at Mar. 31, 2018	$ 23,443	$ 1,079	$ 23,316	$ (2,288)	$ 1,336