Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Hardy - International $ in Millions	Dec. 31, 2017 USD ($) claims	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,309
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	393
IBNR	175
2008
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition						$ 18
Incurred claims and allocated claim adjustment expense, net	13	$ 12	$ 13	$ 13	$ 11	(3)
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented						15
IBNR	$ 1
Cumulative Number of Claims | claims	4,237
2009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition						12
Incurred claims and allocated claim adjustment expense, net	$ (3)	(2)	1	(4)	7	0
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented						12
IBNR	$ 0
Cumulative Number of Claims | claims	3,852
2010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition						49
Incurred claims and allocated claim adjustment expense, net	$ 52	53	47	53	48	(10)
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented						39
IBNR	$ (1)
Cumulative Number of Claims | claims	4,524
2011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition						126
Incurred claims and allocated claim adjustment expense, net	$ 140	140	140	136	136	0
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented						126
IBNR	$ (2)
Cumulative Number of Claims | claims	6,228
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Claim Adjustment Expense Reserves at Acquisition						34
Incurred claims and allocated claim adjustment expense, net	$ 115	114	121	113	106	71
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented						$ 105
IBNR	$ (1)
Cumulative Number of Claims | claims	6,863
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 142	141	140	148	$ 133
IBNR	$ 1
Cumulative Number of Claims | claims	7,525
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 172	179	185	$ 187
IBNR	$ (2)
Cumulative Number of Claims | claims	7,954
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 180	182	$ 192
IBNR	$ 9
Cumulative Number of Claims | claims	8,578
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 251	$ 232
IBNR	$ 53
Cumulative Number of Claims | claims	8,443
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 247
IBNR	$ 117
Cumulative Number of Claims | claims	6,508