Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based Compensation Arrangements Activity
Stock-based compensation expense	$ 89	$ 86	$ 77
Tax benefit recognized on stock-based compensation expense	19	18	27
Tax benefit realized for tax deductions resulting from exercises and vestings	17	32	44
Effect of tax deductions in excess of recognized stock-based compensation expense	7	20	24
Restricted Stock [Member]
Stock-based Compensation Arrangements Activity
Stock-based compensation expense	$ 64	$ 63	$ 58
Number of Shares
Beginning balance (shares)	1,176,578
Granted (shares)	677,482
Vested (shares)	(757,217)
Forfeited (shares)	(4,989)
Ending balance (shares)	1,091,854	1,176,578
Weighted- Average Grant-Date Fair Value Per Share
Beginning balance (in usd per share)	$ 80.70
Granted (in usd per share)	98.75	$ 92.12	$ 79.32
Vested (in usd per share)	78.54
Forfeited (in usd per share)	83.18
Ending balance (in usd per share)	$ 93.38	$ 80.70
Vested Awards Other Than Options Rollforward
Fair value of restricted stock vested (in millions)	$ 74	$ 80	$ 71
Stock Based Compensation (Textual)
Vesting period of stock-based payment awards granted	3 years
Unrecognized share-based compensation cost related to outstanding unvested awards	$ 59
Weighted-average period of recognition for unrecognized compensation costs on nonvested awards	2 years
Restricted Stock Awards - Nonemployee [Member]
Stock Based Compensation (Textual)
Vesting period of stock-based payment awards granted	3 years
Performance Awards [Member]
Stock-based Compensation Arrangements Activity
Stock-based compensation expense	$ 23	22	19
Stock Options and Other Awards [Member]
Stock-based Compensation Arrangements Activity
Stock-based compensation expense	$ 2	$ 1	$ 0
Omnibus Stock Incentive Plan [Member] | Share-based Payment Arrangement [Member]
Stock Based Compensation (Textual)
Number of shares of common stock available to be awarded under stock-based compensation plans (shares)	7,740,665
Formerly Maintained Plans [Member] | Share-based Payment Arrangement [Member]
Stock Based Compensation (Textual)
Number of shares of common stock available to be awarded under stock-based compensation plans (shares)	0