Schedule I - Condensed Financial Information of Parent (Guarantees and Letters of Credit) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) agreement
Condensed Financial Statements, Captions [Line Items]
Obligations maximum exposure, total	$ 490,000,000
Obligations number of agreements | agreement	26
Parent Company
Condensed Financial Statements, Captions [Line Items]
Letter of credit, fee range minimum	0.20%
Letter of credit, fee range maximum	2.50%
Guarantees
Condensed Financial Statements, Captions [Line Items]
Obligations maximum exposure, total	$ 369,000,000
Obligations number of agreements | agreement	14
Guarantees | Parent Company
Condensed Financial Statements, Captions [Line Items]
Obligations, Minimum Individual Exposures	$ 1,000,000
Obligations, individual exposures (minimum less than $1 million)	$ 53,000,000
Guarantees and Asset Sale Related Indemnities (Combined) [Member]
Condensed Financial Statements, Captions [Line Items]
Obligations number of agreements | agreement	15
Guarantees and Asset Sale Related Indemnities (Combined) [Member] | Parent Company
Condensed Financial Statements, Captions [Line Items]
Obligations maximum exposure, total	$ 396,000,000
Letter of Credit
Condensed Financial Statements, Captions [Line Items]
Obligations number of agreements | agreement	7
Letters of credit outstanding	$ 62,000,000
Letter of Credit | Parent Company
Condensed Financial Statements, Captions [Line Items]
Obligations, Minimum Individual Exposures	1,000,000
Obligations, individual exposures (minimum less than $1 million)	29,000,000
Cash Collateralized Letters Of Credit
Condensed Financial Statements, Captions [Line Items]
Obligations maximum exposure, total	$ 32,000,000
Obligations number of agreements | agreement	4
Cash Collateralized Letters Of Credit | Parent Company
Condensed Financial Statements, Captions [Line Items]
Obligations maximum exposure, total	$ 32,000,000
Obligations, Minimum Individual Exposures	1,000,000
Obligations, individual exposures (minimum less than $1 million)	$ 15,000,000