Borrowings - Senior Notes (Details) - USD ($)	1 Months Ended			8 Months Ended	12 Months Ended
	Nov. 30, 2021	Mar. 31, 2013	Jan. 31, 2013	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	May 31, 2021	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2014
Debt Instrument [Line Items]
Debt principal amount				$ 2,097,600,000	$ 2,097,600,000	$ 1,981,100,000
Fair Value				$ 5,811,000,000	5,811,000,000	5,563,000,000
Interest Expense					$ 77,800,000	$ 78,900,000	$ 67,700,000
3.875% Senior Notes Due 2/01/2023
Debt Instrument [Line Items]
Interest rate on senior notes	3.875%			3.875%	3.875%	3.875%
Debt principal amount				$ 0	$ 0	$ 250,000,000.0
5.625% Senior Notes Due 3/30/2043
Debt Instrument [Line Items]
Interest rate on senior notes				5.625%	5.625%
Debt principal amount				$ 600,000,000.0	$ 600,000,000.0	600,000,000.0
5.650% Senior Notes Due 9/15/2048
Debt Instrument [Line Items]
Interest rate on senior notes				5.65%	5.65%
Debt principal amount				$ 350,000,000.0	$ 350,000,000.0	$ 350,000,000.0
3.500% Senior Notes Due 9/19/2029
Debt Instrument [Line Items]
Interest rate on senior notes				3.50%	3.50%	3.50%
Debt principal amount				$ 425,000,000.0	$ 425,000,000.0	$ 425,000,000.0
4.625% Subordinated Notes Due 5/15/2061
Debt Instrument [Line Items]
Interest rate on senior notes									4.625%
Debt principal amount								$ 65,000,000	$ 435,000,000
Fair Value				506,000,000.0	$ 506,000,000.0
Interest Expense				$ 14,800,000
Period from tax redemption event that debt may be redeemed					120 days
Period from rating agency event that debt may be redeemed					90 days
Debt redemption price percentage					102.00%
Senior Notes | 3.875% Senior Notes Due 2/01/2023
Debt Instrument [Line Items]
Repurchased face amount	$ 250,000,000
Senior Notes
Debt Instrument [Line Items]
Interest Expense	$ 10,100,000
Debt redemption price percentage					100.00%
Senior Notes | 3.875% Senior Notes Due 2/01/2023
Debt Instrument [Line Items]
Interest rate on senior notes	3.875%			3.875%	3.875%
Debt principal amount				$ 0	$ 0
Fair Value				$ 0	0	270,000,000.0
Interest Expense					$ 8,900,000	9,900,000	9,900,000
Senior notes percentage of par value			99.966%
Senior Notes | 3.875% Senior Notes Due 2/01/2023 | Treasury Rate
Debt Instrument [Line Items]
Applicable margin over base rate			0.30%
Senior Notes | 5.625% Senior Notes Due 3/30/2043
Debt Instrument [Line Items]
Interest rate on senior notes				5.625%	5.625%
Debt principal amount		$ 400,000,000		$ 600,000,000.0	$ 600,000,000.0							$ 200,000,000
Fair Value				$ 795,500,000	795,500,000	782,600,000
Interest Expense					$ 33,700,000	33,800,000	33,700,000
Senior notes percentage of par value		99.583%										104.315%
Senior Notes | 5.625% Senior Notes Due 3/30/2043 | Treasury Rate
Debt Instrument [Line Items]
Applicable margin over base rate		0.40%
Senior Notes | 5.650% Senior Notes Due 9/15/2048
Debt Instrument [Line Items]
Interest rate on senior notes				5.65%	5.65%
Debt principal amount				$ 350,000,000.0	$ 350,000,000.0
Fair Value				$ 484,700,000	484,700,000	469,300,000
Interest Expense					$ 19,900,000	19,900,000	19,900,000
Senior notes percentage of par value										99.841%	99.914%
Senior Notes | 5.650% Senior Notes Due 9/15/2048 | Treasury Rate
Debt Instrument [Line Items]
Applicable margin over base rate		0.40%
Senior Notes | 3.500% Senior Notes Due 9/19/2029
Debt Instrument [Line Items]
Interest rate on senior notes				3.50%	3.50%
Debt principal amount				$ 425,000,000.0	$ 425,000,000.0
Fair Value				$ 457,400,000	457,400,000	476,600,000
Interest Expense					$ 15,300,000	$ 15,300,000	$ 4,200,000
Senior Notes | 3.500% Senior Notes Due 9/19/2029 | Treasury Rate
Debt Instrument [Line Items]
Applicable margin over base rate			0.30%