Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 300,000
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(3,100,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	0
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	3,367,800,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	4,487,200,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	4,847,500,000
Common Stock [Member]
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	1,600,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	1,700,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	$ 1,700,000
Common Stock, Shares, Outstanding	us-gaap_CommonStockSharesOutstanding	166,858,000
Common Stock, Shares, Outstanding	us-gaap_CommonStockSharesOutstanding	162,202,000
Common Stock, Shares, Outstanding	us-gaap_CommonStockSharesOutstanding	173,754,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 16,300,000
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(3,100,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(600,000)
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	576,700,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	650,100,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	193,500,000
Common Stock Including Additional Paid in Capital [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	900,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	2,995,000,000.0
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	3,213,000,000.0
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	3,073,300,000
AOCI Attributable to Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	0
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(16,300,000)
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	1,195,800,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	177,700,000
Stockholders' Equity Attributable to Parent, Adjusted Balance	cno_StockholdersEquityAttributabletoParentAdjustedBalance	$ 622,400,000