Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	$ 4,285	$ 4,366	$ 4,167
Total net liability for unpaid claim and claim adjustment expenses	17,965	18,070	18,249	$ 18,576
International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,524	1,432
Hardy | International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	1,094
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	456
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2009	0
Liability for unallocated claim adjustment expenses for accident years presented	9
Total net liability for unpaid claim and claim adjustment expenses	465
Hardy | International | 2009
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	(4)	(5)	(4)	(4)	$ (4)	$ (2)	$ 2
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							12
Hardy | International | 2010
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	46	48	47	45	42	35	19
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							38
Hardy | International | 2011
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	134	132	131	127	123	83	30
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							124
Hardy | International | 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	110	109	106	109	100	79	14
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented							$ 104
Hardy | International | 2013
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	133	130	126	120	101	$ 38
Hardy | International | 2014
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	155	150	141	122	$ 56
Hardy | International | 2015
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	144	129	98	$ 29
Hardy | International | 2016
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	171	144	$ 63
Hardy | International | 2017
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	150	$ 53
Hardy | International | 2018
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 55