Fair Value Measurements (Details) (USD $) | Mar. 31, 2015 | Dec. 31, 2014 |
In Millions, unless otherwise specified |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | $3,005 | $3,025 |
U.S. government and agencies | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 114 | 115 |
State and political subdivisions | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 904 | 948 |
Corporate debt securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 1,771 | 1,820 |
Mortgage-backed/asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 101 | 105 |
Foreign government bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 115 | 37 |
Preferred stock available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 272 | 223 |
Equity securities available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 208 | 145 |
Fair Value, Measurements, Recurring | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total assets | 3,485 | 3,393 |
Fair Value, Measurements, Recurring | U.S. government and agencies | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 114 | 115 |
Fair Value, Measurements, Recurring | State and political subdivisions | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 904 | 948 |
Fair Value, Measurements, Recurring | Corporate debt securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 1,771 | 1,820 |
Fair Value, Measurements, Recurring | Mortgage-backed/asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 101 | 105 |
Fair Value, Measurements, Recurring | Foreign government bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 115 | 37 |
Fair Value, Measurements, Recurring | Preferred stock available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 272 | 223 |
Fair Value, Measurements, Recurring | Equity securities available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 208 | 145 |
Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total assets | 261 | 195 |
Fair Value, Measurements, Recurring | Level 1 | U.S. government and agencies | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | State and political subdivisions | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Mortgage-backed/asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Foreign government bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Preferred stock available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 62 | 50 |
Fair Value, Measurements, Recurring | Level 1 | Equity securities available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 199 | 145 |
Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total assets | 3,224 | 3,198 |
Fair Value, Measurements, Recurring | Level 2 | U.S. government and agencies | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 114 | 115 |
Fair Value, Measurements, Recurring | Level 2 | State and political subdivisions | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 904 | 948 |
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 1,771 | 1,820 |
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed/asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 101 | 105 |
Fair Value, Measurements, Recurring | Level 2 | Foreign government bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 115 | 37 |
Fair Value, Measurements, Recurring | Level 2 | Preferred stock available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 210 | 173 |
Fair Value, Measurements, Recurring | Level 2 | Equity securities available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 9 | 0 |
Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total assets | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | U.S. government and agencies | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | State and political subdivisions | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed/asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Foreign government bonds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Available for sale debt securities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Preferred stock available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Equity securities available for sale | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity securities available for sale, at fair value | $0 | $0 |