Schedule I - Summary of Investments - Other Than Investments in Related Parties (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Summary of Investments - Other Than Investments in Related Parties
Cost	$ 63,671.7
Amount as shown in the Consolidated Statement of Financial Position	66,756.9
U.S. government and agencies | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	818.2
Value	780.5
Amount as shown in the Consolidated Statement of Financial Position	780.5
States and political subdivisions | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	3,622.8
Value	3,658.0
Amount as shown in the Consolidated Statement of Financial Position	3,658.0
Non-U.S. governments | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	853.2
Value	996.8
Amount as shown in the Consolidated Statement of Financial Position	996.8
Public utilities | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	4,846.6
Value	4,424.0
Amount as shown in the Consolidated Statement of Financial Position	4,424.0
Redeemable preferred stock | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	37.8
Value	41.2
Amount as shown in the Consolidated Statement of Financial Position	41.2
All other corporate bonds | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	25,396.2
Value	27,453.8
Amount as shown in the Consolidated Statement of Financial Position	27,453.8
Residential mortgage-backed pass-through securities | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	2,799.1
Value	2,845.2
Amount as shown in the Consolidated Statement of Financial Position	2,845.2
Commercial mortgage-backed securities | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	4,078.0
Value	4,026.4
Amount as shown in the Consolidated Statement of Financial Position	4,026.4
Collateralized debt obligations | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	391.9
Value	363.4
Amount as shown in the Consolidated Statement of Financial Position	363.4
Other debt obligations | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	4,157.5
Value	4,167.8
Amount as shown in the Consolidated Statement of Financial Position	4,167.8
Fixed maturities | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	47,001.3
Value	48,757.1
Amount as shown in the Consolidated Statement of Financial Position	48,757.1
Fixed maturities | Trading
Summary of Investments - Other Than Investments in Related Parties
Cost	563.1
Value	563.1
Amount as shown in the Consolidated Statement of Financial Position	563.1
Common stocks: Banks, trust and insurance companies | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	60.8
Value	51.1
Amount as shown in the Consolidated Statement of Financial Position	51.1
Common stocks: Industrial, miscellaneous and all other | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	7.7
Value	10.2
Amount as shown in the Consolidated Statement of Financial Position	10.2
Non-redeemable preferred stock | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	45.3
Value	49.2
Amount as shown in the Consolidated Statement of Financial Position	49.2
Equity securities | Available-for-sale
Summary of Investments - Other Than Investments in Related Parties
Cost	113.8
Value	110.5
Amount as shown in the Consolidated Statement of Financial Position	110.5
Equity securities | Trading
Summary of Investments - Other Than Investments in Related Parties
Cost	716.9
Value	716.9
Amount as shown in the Consolidated Statement of Financial Position	716.9
Mortgage loans
Summary of Investments - Other Than Investments in Related Parties
Cost	11,603.3
Amount as shown in the Consolidated Statement of Financial Position	11,533.6
Real estate acquired in satisfaction of debt
Summary of Investments - Other Than Investments in Related Parties
Cost	213.6
Amount as shown in the Consolidated Statement of Financial Position	213.8
Other real estate
Summary of Investments - Other Than Investments in Related Parties
Cost	1,058.0
Amount as shown in the Consolidated Statement of Financial Position	1,057.8
Policy loans
Summary of Investments - Other Than Investments in Related Parties
Cost	859.7
Amount as shown in the Consolidated Statement of Financial Position	859.7
Investments: Other investments
Summary of Investments - Other Than Investments in Related Parties
Cost	1,542.0
Amount as shown in the Consolidated Statement of Financial Position	$ 2,944.4