Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_UnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Debt - Schedule of Debt (Details) - USD ($)	6 Months Ended
Debt - Schedule of Debt (Details) - USD ($)	Jun. 30, 2020	Mar. 27, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Carrying Value	$ 2,208,000,000.0		$ 2,006,900,000
Senior Notes \| Floating Rate Senior Notes due March 2021
Debt Instrument [Line Items]
Principal Amount	50,000,000.0		50,000,000.0
Carrying Value	$ 49,900,000		49,900,000
Senior Notes \| Floating Rate Senior Notes due March 2021 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate, basis spread	1.25%
Senior Notes \| 4.00% Senior Notes due March 2023
Debt Instrument [Line Items]
Principal Amount	$ 350,000,000.0		350,000,000.0
Carrying Value	$ 348,700,000		348,500,000
Interest rate	4.00%
Senior Notes \| 4.20% Senior Notes due September 2023
Debt Instrument [Line Items]
Principal Amount	$ 300,000,000.0		300,000,000.0
Carrying Value	$ 298,100,000		297,800,000
Interest rate	4.20%
Senior Notes \| 4.90% Senior Notes due March 2028
Debt Instrument [Line Items]
Principal Amount	$ 300,000,000.0		300,000,000.0
Carrying Value	$ 297,000,000.0		296,800,000
Interest rate	4.90%
Senior Notes \| 3.70% Senior Notes due February 2030
Debt Instrument [Line Items]
Principal Amount	$ 350,000,000.0		350,000,000.0
Carrying Value	$ 346,900,000		346,800,000
Interest rate	3.70%
Senior Notes \| 6.75% Senior Notes due February 2034
Debt Instrument [Line Items]
Principal Amount	$ 275,000,000.0		275,000,000.0
Carrying Value	$ 272,200,000		272,100,000
Interest rate	6.75%
Subordinated notes \| 7.00% Fixed-to-Floating Rate Subordinated Notes due March 2048
Debt Instrument [Line Items]
Principal Amount	$ 400,000,000.0		400,000,000.0
Carrying Value	$ 395,200,000		395,000,000.0
Interest rate	7.00%
Subordinated notes \| 7.00% Fixed-to-Floating Rate Subordinated Notes due March 2048 \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate, basis spread	4.135%
Total Senior and Subordinated Notes
Debt Instrument [Line Items]
Carrying Value	$ 2,008,000,000.0		2,006,900,000
Floating Rate Loan \| Floating Rate Loan under the Credit Facility \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Interest rate, basis spread	1.50%
Revolving Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Principal Amount	$ 200,000,000.0		0
Carrying Value	$ 200,000,000.0	$ 200,000,000.0	$ 0