Debt (Narrative) (Details) (USD $)	12 Months Ended					9 Months Ended							12 Months Ended			12 Months Ended			12 Months Ended					9 Months Ended		9 Months Ended					9 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 25, 2013 7.500%, due 2019 [Member]	Aug. 01, 2012 Senior Unsecured Notes [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member] 2.300%, due 2018 [Member]	Jul. 30, 2013 Senior Unsecured Notes [Member] 2.300%, due 2018 [Member]	Jul. 30, 2013 Senior Unsecured Notes [Member] 5.100%, due 2044 [Member]	Sep. 10, 2012 Senior Unsecured Notes [Member] 1.250%, due 2015 [Member]	Sep. 10, 2012 Senior Unsecured Notes [Member] 1.875%, due 2018 [Member]	Sep. 10, 2012 Senior Unsecured Notes [Member] 3.300%, due 2023 [Member]	Sep. 10, 2012 Senior Unsecured Notes [Member] 4.650%, due 2043 [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] 6.800%, due 2012 [Member]	May 07, 2012 Senior Unsecured Notes [Member] 3.125%, due 2022 [Member]	May 07, 2012 Senior Unsecured Notes [Member] 4.625%, due 2042 [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] 6.375%, due 2012 [Member]	Jan. 17, 2012 Senior Unsecured Notes [Member] 6.375%, due 2012 [Member]	Oct. 02, 2012 Senior Convertible Debentures [Member]	Dec. 31, 2013 Senior Convertible Debentures [Member] 2.750%, due 2042 [Member]	Oct. 09, 2012 Senior Convertible Debentures [Member] 2.750%, due 2042 [Member]	Oct. 02, 2012 Senior Convertible Debentures [Member] 2.750%, due 2042 [Member]	Dec. 31, 2013 Federal Home Loan Bank Advances [Member]	Dec. 31, 2012 Federal Home Loan Bank Advances [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member] 6.000%, due 2014 [Member]	Sep. 05, 2013 Senior Unsecured Notes [Member] 6.000%, due 2014 [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member] Tender Offer [Member]	Aug. 13, 2013 Senior Unsecured Notes, First Tender Offer Tranche [Member]	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche [Member]	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche [Member] 5.875%, due 2017 [Member]	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche [Member] 7.000%, due 2019 [Member]	Sep. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member]	Aug. 13, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member]	Aug. 12, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member]	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member]	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member] 5.950%, due 2034 [Member]	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member] 5.850%, due 2036 [Member]	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member] 6.375%, due 2037 [Member]	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche [Member] 5.800%, due 2040 [Member]	Dec. 24, 2012 Amerigroup [Member] Senior Unsecured Notes [Member] 7.500%, due 2019 [Member]
Debt Instrument [Line Items]
Short-term FHLB borrowings outstanding	$ 400,000,000	$ 250,000,000
Debt instrument interest rate					6.80%		2.30%	5.10%	1.25%	1.875%	3.30%	4.65%		3.125%	4.625%		6.375%		2.75%	2.75%		0.17%	0.206%		6.00%				5.875%	7.00%					5.95%	5.85%	6.375%	5.80%	7.50%
Debt redemption date																								Sep. 05, 2013		Aug. 13, 2013
Repurchased face amount																									400,000,000.0		300,000,000.0					400,000,000.0
Early repayment of senior debt																								411,000,000		837,700,000
Loss on extinguishment of debt	145,300,000	0	0																					10,000,000		135,300,000
Tender offer initiation date																										Jul. 30, 2013
Repurchase tender offer, maximum amount																												300,000,000.0						300,000,000
Repurchase tender offer, additional amount of increase																												100,000,000						100,000,000.0
Date of increase to tender offer																															Aug. 12, 2013
Repurchase tender offer, maximum amount after increase																																	400,000,000.0
Issue date						Jul. 30, 2013
Long-term debt face amount	1,500,000,000						650,000,000.0	600,000,000.0	625,000,000.0	625,000,000.0	1,000,000,000.0	1,000,000,000.0		850,000,000.0	900,000,000.0					1,500,000,000.0																			475,000,000.0
Maturity date on long-term debt																			Oct. 15, 2042
Repayments of Senior Debt													800,000,000			350,000,000
Estimated fair value																																							556,900,000
Debt Redemption				555,600,000
Redemption Percent				117.00%
Line of credit facility, maximum borrowing capacity	2,000,000,000.0
Line of Credit Maturity Date	Sep. 29, 2016
Line of credit facility, amount ouststanding	0	0
Commercial paper authorized	2,500,000,000.0
Weighted average interest rate on commercial paper borrowings	0.42%	0.396%
Convertible Debt [Abstract]
Number of trading days in 30 day period greater than 130%	20 years
Number of trading days exceeding 130%	30 days
Product of Conversion to Stock Price	130.00%
Required days trading price less than 98%	5 days
Measurement Period for testing	10 days
Percent of Conversion Price to Closing Price	98.00%
Earliest Date for Conversion	Apr. 15, 2042
Date debentures redeemable at our option																			Oct. 20, 2022
Initial conversion rate (per $1000 of principal)	13.2917																		13.2319
Conversion premium (%)																		0.250
Closing Price Company Stock																			$ 92.39		$ 60.46
If-converted value per dollar above the conversion price																			342,000,000
Initial conversion price (per share of stock)	$ 75.2345																				$ 75.575
Amount of debenture proceeds to repurchase stock																		371,000,000
Amortization period debt discount	29 years
Effective interest rate																			5.13%
Debentures Interest Expense																			49,200,000
Stated Interest Expense																			41,300,000
Debenture Amortization Expense																			7,900,000
Interest paid	597,200,000	479,100,000	432,900,000
Future maturities of debt in 2014	897,200,000
Future maturities of debt in 2015	624,900,000
Future maturities of debt in 2016	1,109,600,000
Future maturities of debt in 2017	944,700,000
Future maturities of debt in 2018	1,262,000,000
Future maturities of debt Thereafter	$ 9,253,200,000