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, 2019	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 2010	$ 4,584	$ 4,285	$ 4,366
Total net liability for unpaid claim and claim adjustment expenses	17,885	17,965	18,070	$ 18,249
International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,628	1,524
Hardy | International
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	1,339
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	461
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2010	3
Liability for unallocated claim adjustment expenses for accident years presented	9
Total net liability for unpaid claim and claim adjustment expenses	473
Hardy | International | 2010
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	47	47	49	48	$ 45	$ 43	$ 36	$ 19
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented								39
Hardy | International | 2011
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	137	136	134	133	129	124	84	31
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented								125
Hardy | International | 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	111	110	109	107	109	100	80	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	138	134	131	127	121	102	$ 38
Hardy | International | 2014
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	162	157	151	142	123	$ 56
Hardy | International | 2015
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	158	145	130	98	$ 30
Hardy | International | 2016
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	182	172	145	$ 63
Hardy | International | 2017
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	184	151	$ 53
Hardy | International | 2018
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	176	$ 55
Hardy | International | 2019
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 44