Concentrations of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Japan Government and Agencies Securities [Member]
Amortized Cost	$ 69,968	$ 62,094
Fair Value	74,955	65,757
Japan Government and Agencies Securities [Member] | Available-for-sale Securities [Member]
Amortized Cost	65,817	60,323
Fair Value	70,647	63,846
Japan Government and Agencies Securities [Member] | Held-to-maturity Securities [Member]
Amortized Cost	1,242	1,260
Fair Value	1,382	1,388
Japan Government and Agencies Securities [Member] | Trading Account Assets Supporting Insurance Liabilities [Member]
Amortized Cost	552	471
Fair Value	569	483
Japan Government and Agencies Securities [Member] | Other Trading [Member]
Amortized Cost	41	40
Fair Value	41	40
Japan Government and Agencies Securities [Member] | Short-term Investments [Member]
Amortized Cost	0	0
Fair Value	0	0
Japan Government and Agencies Securities [Member] | Cash and Cash Equivalents [Member]
Amortized Cost	2,316	0
Fair Value	2,316	0
South Korean government and Agency Securities [Member]
Amortized Cost	5,407	4,697
Fair Value	6,620	5,260
South Korean government and Agency Securities [Member] | Available-for-sale Securities [Member]
Amortized Cost	5,405	4,678
Fair Value	6,618	5,240
South Korean government and Agency Securities [Member] | Held-to-maturity Securities [Member]
Amortized Cost	0	0
Fair Value	0	0
South Korean government and Agency Securities [Member] | Trading Account Assets Supporting Insurance Liabilities [Member]
Amortized Cost	0	17
Fair Value	0	18
South Korean government and Agency Securities [Member] | Other Trading [Member]
Amortized Cost	2	2
Fair Value	2	2
South Korean government and Agency Securities [Member] | Short-term Investments [Member]
Amortized Cost	0	0
Fair Value	0	0
South Korean government and Agency Securities [Member] | Cash and Cash Equivalents [Member]
Amortized Cost	0	0
Fair Value	$ 0	$ 0