Derivative Financial Instruments - Narrative (Details)	9 Months Ended
	Sep. 30, 2019 USD ($) entity contract	Dec. 31, 2018 contract	Sep. 30, 2018 contract
Derivative [Line Items]
Potential recoveries under credit risk derivatives | $	$ 0
Number of derivatives held (contract)	6,930	7,062
Cash and securities pledged as collateral by counterparties | $	$ 14,000,000
Cash and securities pledged as collateral to counterparties | $	0
Securities pledged in the form of margin deposits | $	$ 6,000,000
Term of credit default swaps (in years)	5 years
The number of reference entities generally included in a CDX index | entity	125
Fair Value Hedging | Derivatives designated as fair value accounting hedging instruments
Derivative [Line Items]
Number of derivatives held (contract)	1		1
Number of foreign currency contracts	0		0
Cash Flow Hedging | Derivatives designated as fair value accounting hedging instruments
Derivative [Line Items]
Number of derivatives held (contract)	0		0
Number of foreign currency contracts			1