Consolidating Financial Statements (Details) - Consolidating Statement of Income (Unaudited) - USD ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Consolidating Statement of Income
Premiums		$ 6,855,000,000	$ 6,537,000,000
Net investment income		582,000,000	603,000,000
Fee income		109,000,000	103,000,000
Net realized investment gains (losses)	[1]	53,000,000	(11,000,000)
Other revenues		72,000,000	54,000,000
Total revenues		7,671,000,000	7,286,000,000
Claims and claim adjustment expenses		4,442,000,000	4,296,000,000
Amortization of deferred acquisition costs		1,117,000,000	1,061,000,000
General and administrative expenses		1,057,000,000	1,062,000,000
Interest expense		88,000,000	89,000,000
Total claims and expenses		6,704,000,000	6,508,000,000
Income before income taxes		967,000,000	778,000,000
Income tax expense (benefit)		171,000,000	109,000,000
Net income		796,000,000	669,000,000
Total other-than-temporary impairment gains (losses)		(1,000,000)	0
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(1,000,000)	0
Other-than-temporary impairment losses recognized in other comprehensive income (loss)		0
Other-than-temporary impairment gains recognized in other comprehensive income (loss)			0
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Income
Premiums		4,689,000,000	4,468,000,000
Net investment income		416,000,000	412,000,000
Fee income		109,000,000	103,000,000
Net realized investment gains (losses)		22,000,000	2,000,000
Other revenues		38,000,000	27,000,000
Total revenues		5,274,000,000	5,012,000,000
Claims and claim adjustment expenses		3,024,000,000	2,910,000,000
Amortization of deferred acquisition costs		745,000,000	705,000,000
General and administrative expenses		722,000,000	729,000,000
Interest expense		12,000,000	11,000,000
Total claims and expenses		4,503,000,000	4,355,000,000
Income before income taxes		771,000,000	657,000,000
Income tax expense (benefit)		146,000,000	106,000,000
Net income		625,000,000	551,000,000
Total other-than-temporary impairment gains (losses)		(1,000,000)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(1,000,000)
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Income
Premiums		2,166,000,000	2,069,000,000
Net investment income		155,000,000	185,000,000
Net realized investment gains (losses)		15,000,000	(12,000,000)
Other revenues		34,000,000	28,000,000
Total revenues		2,370,000,000	2,270,000,000
Claims and claim adjustment expenses		1,418,000,000	1,386,000,000
Amortization of deferred acquisition costs		372,000,000	356,000,000
General and administrative expenses		330,000,000	328,000,000
Total claims and expenses		2,120,000,000	2,070,000,000
Income before income taxes		250,000,000	200,000,000
Income tax expense (benefit)		42,000,000	32,000,000
Net income		208,000,000	168,000,000
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Income
Net investment income		11,000,000	6,000,000
Net realized investment gains (losses)		16,000,000	(1,000,000)
Total revenues		27,000,000	5,000,000
General and administrative expenses		5,000,000	6,000,000
Interest expense		76,000,000	78,000,000
Total claims and expenses		81,000,000	84,000,000
Income before income taxes		(54,000,000)	(79,000,000)
Income tax expense (benefit)		(17,000,000)	(29,000,000)
Net income of subsidiaries		833,000,000	719,000,000
Net income		796,000,000	669,000,000
Eliminations [Member]
Consolidating Statement of Income
Other revenues			(1,000,000)
Total revenues			(1,000,000)
General and administrative expenses			(1,000,000)
Total claims and expenses			(1,000,000)
Net income of subsidiaries		(833,000,000)	(719,000,000)
Net income		$ (833,000,000)	$ (719,000,000)

[1] Total other-than-temporary impairment (OTTI) gains (losses) were $(1) million and $0 for the three months ended March 31, 2019 and 2018, respectively. Of total OTTI, credit losses of $(1) million and $0 for the three months ended March 31, 2019 and 2018, respectively, were recognized in net realized investment gains (losses). In addition, unrealized gains (losses) from other changes in total OTTI of $0 for each of the three months ended March 31, 2019 and 2018, respectively, were recognized in other comprehensive income (loss) as part of changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income.