Senior Notes, Convertible Notes and Trust Preferred Securities - Schedule of Debt Instrument Redemptions (Details)	Dec. 31, 2015 USD ($)
Senior Notes [Member]
Debt Instrument, Redemption [Line Items]
Face Amount	$ 500,000,000
4.40% Senior Note [Member] \| Senior Notes Due 2024 [Member]
Debt Instrument, Redemption [Line Items]
Face Amount	$ 250,000,000
Interest Rate	4.40%
Issue Price	99.883%
4.25% Senior Note [Member] \| Senior Notes Due 2023 [Member]
Debt Instrument, Redemption [Line Items]
Face Amount	$ 250,000,000
Interest Rate	4.25%
Issue Price	99.026%

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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