Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - International - Hardy - USD ($) $ in Millions	12 Months Ended						24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016
2008
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 1	$ (1)	$ 0	$ 2	$ (4)	$ (3)				$ (5)
2009
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	(3)	5	(11)	(5)	0				(15)
2010
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	6	(6)	5	9	(10)				3
2011
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	0	0	4	0	10	$ 0				14
2012
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	(7)	8	7	$ 1					$ 10
2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	1	(8)	$ 15					$ 9
2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(7)	(6)	$ (2)					$ (15)
2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(2)	$ (10)					$ (12)
2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ 19