Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Status of nonvested restricted stock
Net impact due to stock awards modification	$ 0		$ (4)	$ 2	$ (4)
Restricted Stock [Member]
Restricted stock compensation expense
Restricted stock compensation expense	7		5	14	12
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 53			$ 53
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition				2 years 1 month 6 days
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,775,000	1,516,000		1,516,000
Nonvested shares subject to restriction, weighted average exercise price	$ 44.77	$ 42.97		$ 42.97
Restricted shares granted to employees	125,000	930,000		1,031,513
Granted shares subject to restriction, weighted average exercise price	$ 40.78	$ 41.92
Shares subject to restriction, Vested	(28,000)	(665,000)
Vested shares subject to restriction, weighted average exercise price	$ 50.43	$ 35.94
Shares subject to restriction, Forfeited	(37,000)	(6,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 45.13	$ 45.41
Nonvested shares subject to restriction, Ending Balance	1,835,000	1,775,000		1,835,000
Nonvested shares subject to restriction, weighted average exercise price	$ 44.40	$ 44.77		$ 44.40
Performance Shares [Member]
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	478,000	297,000		297,000
Nonvested shares subject to restriction, weighted average exercise price	$ 56.93	$ 60.35		$ 60.35
Restricted shares granted to employees	5,000	190,000
Granted shares subject to restriction, weighted average exercise price	$ 51.59	$ 51.52
Shares subject to restriction, Forfeited	(56,000)	(9,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 55.67	$ 55.30
Nonvested shares subject to restriction, Ending Balance	427,000	478,000		427,000
Nonvested shares subject to restriction, weighted average exercise price	$ 57.03	$ 56.93		$ 57.03
Performance share compensation expense				$ 3	2
Relative Revenue Growth Performance Share Plans [Member]
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	478,000	297,000		297,000
Nonvested shares subject to restriction, weighted average exercise price	$ 45.04	$ 47.03		$ 47.03
Restricted shares granted to employees	5,000	190,000
Granted shares subject to restriction, weighted average exercise price	$ 41.92	$ 41.90
Shares subject to restriction, Forfeited	(56,000)	(9,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 44.24	$ 44.12
Nonvested shares subject to restriction, Ending Balance	427,000	478,000		427,000
Nonvested shares subject to restriction, weighted average exercise price	$ 45.11	$ 45.04		$ 45.11
Performance share compensation expense	$ 1		$ 1		$ 8
2018 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	7,000,000			7,000,000
Number of shares available for grant	6,000,000			6,000,000
First Half Vested | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of awards vested				50.00%
Vesting period				2 years
Second Half Vested | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				3 years
Director [Member] | Restricted Stock [Member]
Status of nonvested restricted stock
Restricted shares granted to employees				23,880