Stock Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Status of nonvested restricted stock
Net impact due to stock awards modification	$ 0			$ 6	$ 2	$ 2
Restricted Stock [Member]
Restricted stock compensation expense
Restricted stock compensation expense	8			7	22	19
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 45				$ 45
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition					1 year 10 months 24 days
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,835,000	1,775,000	1,516,000		1,516,000
Nonvested shares subject to restriction, weighted average exercise price	$ 44.40	$ 44.77	$ 42.97		$ 42.97
Restricted shares granted to employees	22,000	125,000	930,000		1,054,006
Granted shares subject to restriction, weighted average exercise price	$ 36.68	$ 40.78	$ 41.92
Shares subject to restriction, Vested	(7,000)	(28,000)	(665,000)
Vested shares subject to restriction, weighted average exercise price	$ 43.81	$ 50.43	$ 35.94
Shares subject to restriction, Forfeited	(30,000)	(37,000)	(6,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 44.99	$ 45.13	$ 45.41
Nonvested shares subject to restriction, Ending Balance	1,820,000	1,835,000	1,775,000		1,820,000
Nonvested shares subject to restriction, weighted average exercise price	$ 44.29	$ 44.40	$ 44.77		$ 44.29
Performance Shares [Member]
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	427,000	478,000	297,000		297,000
Nonvested shares subject to restriction, weighted average exercise price	$ 57.03	$ 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	(5,000)	(56,000)	(9,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 57.29	$ 55.67	$ 55.30
Nonvested shares subject to restriction, Ending Balance	422,000	427,000	478,000		422,000
Nonvested shares subject to restriction, weighted average exercise price	$ 57.03	$ 57.03	$ 56.93		$ 57.03
Performance share compensation expense	$ 2			3	$ 5	6
Relative Revenue Growth Performance Share Plans [Member]
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	427,000	478,000	297,000		297,000
Nonvested shares subject to restriction, weighted average exercise price	$ 45.11	$ 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	(5,000)	(56,000)	(9,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 44.76	$ 44.24	$ 44.12
Nonvested shares subject to restriction, Ending Balance	422,000	427,000	478,000		422,000
Nonvested shares subject to restriction, weighted average exercise price	$ 45.11	$ 45.11	$ 45.04		$ 45.11
Performance share compensation expense	$ 3			$ 5	$ 3	$ 13
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