CONSOLIDATED QUARTERLY RESULTS - UNAUDITED (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED QUARTERLY RESULTS - UNAUDITED
Premiums and policy fees	$ 871,032	$ 759,038	$ 851,802	$ 815,896	$ 841,255	$ 657,218	$ 756,331	$ 726,847	$ 3,297,768	$ 2,981,651	$ 2,814,278
Reinsurance ceded	(425,780)	(277,136)	(342,968)	(327,713)	(380,625)	(270,730)	(390,490)	(335,350)	(1,373,597)	(1,377,195)	(1,345,836)
Net of reinsurance ceded	445,252	481,902	508,834	488,183	460,630	386,488	365,841	391,497	1,924,171	1,604,456	1,468,442
Net investment income	550,571	558,174	550,816	538,163	539,952	454,275	466,220	457,634	2,197,724	1,918,081	1,862,332
Realized investment gains (losses)	(105,307)	2,621	(11,238)	(34,827)	451	13,137	29,903	(1,344)	(148,751)	42,147	(66,331)
Other income	119,069	105,389	106,931	99,039	116,102	98,794	94,392	85,027	430,428	394,315	358,563
Total revenues	1,009,585	1,148,086	1,155,343	1,090,558	1,117,135	952,694	956,356	932,814	4,403,572	3,958,999	3,623,006
Total benefits and expenses	898,594	963,203	993,133	965,353	943,523	810,573	799,343	815,187	3,820,283	3,368,626	3,170,035
Income before income tax	110,991	184,883	162,210	125,205	173,612	142,121	157,013	117,627	583,289	590,373	452,971
Income tax expense	36,641	65,974	54,233	41,566	54,699	49,060	53,814	39,336	198,414	196,909	150,519
Net Income	$ 74,350	$ 118,909	$ 107,977	$ 83,639	$ 118,913	$ 93,061	$ 103,199	$ 78,291	$ 384,875	$ 393,464	$ 302,452
Net income available to PLC's common shareowners - basic (in dollars per share)	$ 0.92	$ 1.48	$ 1.35	$ 1.05	$ 1.50	$ 1.17	$ 1.30	$ 0.99	$ 4.81	$ 4.96	$ 3.73
Average shares outstanding - basic (in shares)	80,430,799	80,231,591	79,979,153	79,608,461	79,540,583	79,492,274	79,404,770	79,139,392	80,065,217	79,395,622	81,066,338
Net income available to PLC's common shareowners - diluted (in dollars per share)	$ 0.91	$ 1.46	$ 1.33	$ 1.03	$ 1.47	$ 1.15	$ 1.27	$ 0.97	$ 4.73	$ 4.86	$ 3.66
Average shares outstanding - diluted (in shares)	81,714,510	81,458,870	81,446,277	80,872,152	81,053,787	80,852,078	81,087,238	80,706,744	81,375,496	80,925,713	82,723,016