Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Excluding Hardy - International $ in Millions	Dec. 31, 2018 USD ($) claims	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,683
IBNR	546
2009
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	219	$ 216	$ 218	$ 226	$ 236	$ 239	$ 253	$ 253	$ 251	$ 254
IBNR	$ 8
Cumulative Number of Claims | claims	20,257
2010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 184	188	195	201	208	217	223	229	$ 232
IBNR	$ 8
Cumulative Number of Claims | claims	21,949
2011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 216	219	221	227	239	258	266	$ 265
IBNR	$ 9
Cumulative Number of Claims | claims	24,585
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 236	244	251	251	258	273	$ 266
IBNR	$ 20
Cumulative Number of Claims | claims	24,975
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 250	257	261	281	289	$ 287
IBNR	$ 25
Cumulative Number of Claims | claims	23,909
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 271	279	290	290	$ 275
IBNR	$ 38
Cumulative Number of Claims | claims	24,874
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 286	304	305	$ 289
IBNR	$ 51
Cumulative Number of Claims | claims	23,239
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 289	302	$ 284
IBNR	$ 79
Cumulative Number of Claims | claims	17,557
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 363	$ 300
IBNR	$ 134
Cumulative Number of Claims | claims	17,865
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 369
IBNR	$ 174
Cumulative Number of Claims | claims	16,565