Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	$ 670	$ 650	$ 645
Deferred costs	1,635	1,404	1,377
Amortization — DAC	(1,622)	(1,384)	(1,372)
Finite-Lived Intangible Assets, Accumulated Amortization	(299)	(132)
Balance, end of period	785	670	650
Customer Relationships [Member]
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Finite-Lived Intangible Assets, Accumulated Amortization	(92)	(49)
The Navigators Group, Inc. [Member] | Customer Relationships [Member]
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 102	$ 0	$ 0