Stockholders' Equity - Narrative (Detail) - USD ($)			12 Months Ended
	Nov. 05, 2019	Oct. 22, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2018	Dec. 31, 2016
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			10,000,000	10,000,000
Stockholders' equity attributable to parent			$ 11,091,000,000.0	$ 10,508,300,000	$ 10,216,200,000		$ 9,770,400,000
Preferred stock, par value (in dollars per share)
Proceeds from issuance of preferred stock			$ 392,500,000	$ 0	$ 0
Number of shares authorized to be repurchased (in shares)						25,000,000.0
Average price paid per share for common stock repurchased (in dollars per share)			$ 93.40	$ 102.69	$ 90.25
Upper Limit
Class of Stock [Line Items]
Stock repurchase authorized amount			$ 828,500,000
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)			16,000	16,000
Preferred stock, shares issued (in shares)			16,000,000
Per share ownership interest, percentage			0.10%
Stockholders' equity attributable to parent			$ 388,500,000	$ 388,500,000
Preferred stock, par value (in dollars per share)			$ 0
Preferred stock, liquidation preference			$ 25,000
Depository shares, liquidation preference (in dollars per share)			$ 25
Preferred stock, annual dividend rate			5.85%
Preferred stock, dividends per share, declared (in dollars per share)		$ 365.625
Preferred stock			$ 388,500,000	$ 388,500,000
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)			5,000	5,000
Preferred stock, shares issued (in shares)			500,000
Per share ownership interest, percentage			1.00%
Preferred stock, par value (in dollars per share)			$ 0
Preferred stock, liquidation preference			$ 100,000
Depository shares, liquidation preference (in dollars per share)			$ 1,000
Preferred stock, annual dividend rate			4.60%
Preferred stock			$ 493,500,000	$ 493,500,000
Preferred stock, variable rate			3.202%
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)			16,000
Preferred stock, shares issued (in shares)	16,000,000
Per share ownership interest, percentage			0.10%
Preferred stock, par value (in dollars per share)	$ 0
Preferred stock, liquidation preference	$ 25,000
Depository shares, liquidation preference (in dollars per share)	$ 25
Preferred stock, annual dividend rate			4.70%
Preferred stock			$ 391,400,000	$ 0
Proceeds from issuance of preferred stock	$ 391,400,000