Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended			206 Months Ended
	Jan. 14, 2020	Feb. 08, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	May 24, 2018	Dec. 31, 1995
Class Of Stock [Line Items]
Stock repurchase program, number of shares authorized to be repurchased, percent															10.00%	10.00%
Treasury stock, shares, acquired		20,036												39,689,999
Treasury stock, value, acquired, cost method		$ 0.8												$ 1,700.0
Treasury stock acquired, average cost per share														$ 41.57
Treasury stock, shares, retired														33,475,406
Treasury stock, retired, cost method, amount														$ 1,200.0
Treasury stock, shares			330,690				479,407				330,690	479,407		330,690
Stock repurchase program, remaining authorized repurchase amount (in shares)			4,148,935								4,148,935			4,148,935
Cash dividends per share (in dollar per share)			$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 0.55	$ 2.20	$ 2.20	$ 2.20
Subsequent Event [Member]
Class Of Stock [Line Items]
Cash dividends per share (in dollar per share)	$ 0.25
Dividends payable, date declared	Jan. 14, 2020
Dividends payable, date to be paid	Feb. 14, 2020
Dividends payable, date of record	Jan. 24, 2020