Subsequent Events (Details) - Junior Subordinated Debt - Subsequent Event	Oct. 21, 2019 USD ($)
Floating Rate Subordinated Debentures Due 2047
Subsequent Event [Line Items]
Aggregate principal amount	$ 800,000,000
Floating Rate Subordinated Debentures Due 2028
Subsequent Event [Line Items]
Aggregate principal amount	150,000,000
Floating Rate Subordinated Debentures Due 2028 \| Forecast
Subsequent Event [Line Items]
Amount redeemed	$ 50,100,000

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

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=114775744&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

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