Stockholders' Equity (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2017	Nov. 30, 2015
Stockholders' Equity [Line Items]
Available outstanding common stock under repurchase programs		$ 700,000,000
Additional paid-in capital		0	$ 0
Remainder of excess APIC recorded as a reduction to retained earnings		$ 1,025,000,000	$ 1,250,000,000
Percentage Of Change In Dividends Paid Per Share	8.60%
Dividends declared per share		$ 3.77	$ 3.47	$ 3.19
November Two Thousand Fifteen Board of Directors Authorization [Member]
Stockholders' Equity [Line Items]
Stock Repurchase Program, Authorized Amount						$ 2,000,000,000.0
November Two Thousand Seventeen Board of Directors Authorization [Member]
Stockholders' Equity [Line Items]
Stock Repurchase Program, Authorized Amount					$ 2,000,000,000.0